FrankM - Wiki is reasonably accurate as long as the subject is technical and doesn't have to worry about ax grinders. For example, the sections on statistical methods are well done and, as a statistician, I've found their pages a good starting point for those occasions where I've run into a reference to a method I've either not tried or not been aware of. The same holds true for the pages on physics and chemistry.
Another good source for information are the open access peer reviewed journals in almost any field. The thing to bear in mind with articles from these journals is you have to have some sense of the kind of articles they accept. For example, if the journal is one with an applied focus in areas which have seen a lot of research then there is a good chance that whatever you read is up to date and correct. By "correct" I mean that the false positive rate for the papers is low.
On the other hand, if the journal is one that prints recent findings where the authors are just at the beginning of research in some area that hasn't been investigated then most likely the power of these papers is low (as it almost has to be because of time/money/effort issues) and the chances for false positives is high. This isn't a shortcoming, rather it is a fact of the nature of initial investigations into almost anything, but it is something that needs to be remembered.