After seeing a few things around and about on the subject of books and the internet, as far as the beginner is concerned, I figured I'd put a few thoughts of my own together. Books - and other sources - are a tricky subject for the beginner because it's difficult to know where to start, and what to rely on. And especially when that involves looking on the internet.
It's all well and good being pointed towards a book list - even a short one aimed at beginners, like the one on the CR FAQ. I think the books listed there are excellent choices, but one problem a lot of folks have is investing the money in buying those books. There are plenty of places that these kinds of books can be found second hand at more than reasonable prices, but even so, that might be stretching an already non-existent budget too far for many these days.
There's always the option of trying to find them at the library, but that's not necessarily a satisfactory solution if you have to order them through Inter-Library Loan, if that's an option at all (I'm lucky I can get access to an academic library, because a lot of the books I want I couldn't get at my local library, unfortunately). It's important to remember that these books are recommended for a reason - they're not perfect, by any means, but they offer a lot of good information that wll give any fledgling reconstructionist a good start.
In the internet age, though, people are increasingly used to finding answers straight away, and looking things up on Google offers a much quicker and cheaper solution, and it might be tempting to ignore books that aren't freely available in favour of those that are. There are lots of books and articles available online, in full, along with plenty of websites dealing with various kinds of 'Celtic Paganisms' that might appeal to the beginner. The problem with this, of course, is that websites aren't necessarily always reliable or trustworthy, and nor are books. This post here on Discernment offers a lot of good advice on how to approach and assess the reliability of different sources, and Maya's essay here makes a good compliment to that.
The internet can be incredibly useful as a tool for research, if it's used wisely. It can also be a minefield, but knowing where to look - and how - can help narrow things down. Instead of just doing a web search, using Google Scholar can help you find far more reliable sources than you normally would (though I find a lot of neo-pagan sources crop up there as well, and while that might not be so bad for some, they're not necessarily the sort of focus I'm looking for), and while much of it may not be freely available, you can often find a few gems that are downloadable as pdfs. For many, admittedly, this is just a quicker route to a rapidly expanding wishlist...
One of the biggest advantages researching online can offfer is all of those free books, and occasionally articles or journals that are fully available, for free. Again, though, it's a double-edged sword. It's tempting to assume that just because a book seems to be well-written and well-researched, and has an authoritative or academic tone, then it's all good. This isn't always the case, because the author often has their own approach and bias in how they look at the sources, so it often helps to know where they're coming from, and to read as widely as possible in order to try and balance one view, or one approach, with another. Those pointers I've linked to above will come in handy - I think at the most simplest level, the best thing to remember when you're reading something is asking the question where did that come from? Until you know, and can see it's from a good source, look elsewhere as well and try to verify the point. If it seems a little off the wall, it probably is.
When you're reading academic tomes in particular, it helps to know the kind of angle they're coming from. I've outlined some of the approaches to Celtic Studies and Archaeology here already, and bearing this in mind is a good way to make your own mind up on things. Reading books on the same subject from these different approaches might leave you with conflicting views on certain things, and you're going to have to make your own mind up and decide what you think is right. When you start doing your own research, you'll find that there are rarely any quick answers.
There's sometimes a tendency to dismiss older books in favour of newer ones, simply because they're old and therefore out of date. Most of those books and articles that are available online are out of print, and yes, it's a good thing to remember that there's often a lot wrong with older books, simply because of the way approaches to research and interpretation have changed over the years. But that doesn't automatically make new books better, or strip those older books of any value whatsoever. There's a lot of stuff in those older sources that come in very handy to the modern reconstructionist, not least because there are translations of material that have since been relatively ignored. Since these older sources are now out of copyright they are often easily found online, in full, and this is where we come back to the issue of relying on the internet, and these free sources, in our reading.
Aside from Google Scholar, some of the best places to start looking are on archive.org, sacred-texts.com, or Google Books, and there's also a huge library of Scottish-focused books at Electric Scotland as well as lots of books on the Isle of Man at isleofman.com. (Scribd can also be a minefield of useful books, but they're not always books that are copyright free and there's a tendency for them to disappear once they're discovered, so it can be hit or miss.)
And that's nice and all, but when you're being cautioned about these books being potentially problematic sources, where do you start? While I would say that the histories that you can find are often very outdated in approach and you're probably better off sticking with more up to date books, one of the biggest strengths of some of these old sources is that they can contain eye-witness accounts of customs and traditions that have since died out or only continue privately. Many of these can be found in old journals (for example, when I was researching stuff for the Michaelmas struan, I found some particularly useful articles at archive.org).
Alexander Carmichael's Carmina Gadelica is one of the best sources to look if you're wanting inspiration for practices:
There are six volumes in all, but because of the way they were published, over several decades, not all of them are out of copyright yet. The full six volume set will probably set you back a pretty penny, but you can buy an abridged version that just contains the English translations cheaply, which makes a good starting place. With the abridged version you lose the Gàidhlig and the extensive notes/glossary and indexing that you find in the full volume set. Then again, the first two volumes in particular are the most helpful to the aspiring reconstructionist, because later volumes were 'improved' and 'polished' more so than the first two. The volumes available online are therefore perhaps the most helpful for the beginner (though the others shouldn't be ignored, by any means).
Compare Carmichael's work with Douglas Hyde's Religious Songs of Connacht, and you'll see a lot of similarities along the way, which is especially helpful if you want to work out your own songs or prayers and base them on, and it goes to show that what Carmichael recorded on those remote islands can be just as useful for the Irish Reconstructionist as the Scottish, or simply Gaelic (labels are a tricky thing).
Looking on archive.org, you'll find a wealth of good stuff if you look up Folklore journals, or the Celtic Review, or search for well known and prolific authors like Kuno Meyer and Whitley Stokes. Much of this work will be outdated, and especially in the case of the translations provided by Meyer and Stokes, are much in need of looking at again in a modern context. This is happening, but it isn't necessarily widely available, and in the meantime we can find some gems in albeit somewhat imperfect formats.
As for websites, maryjones.us is a great starting point, which is good for a reconstructionist in particular, and links that I've posted previously, like to the Ulster Institutional Repository and the Carmichael Watson Project. Looking at the various universities who offer Celtic Studies as a discipline can also be helpful, such as Ulster, Belfast, Dublin, Glasgow, Edinburgh, Aberdeen, Cambridge, Berkeley, Harvard, and so on. Otherwise - generally speaking - a good way to determine the reliability of a website is that if it actively sparkles, it's probably not too good as far as historical accuracy and research go. References also help.