The next two sites I want to cover are places that you go for learning about stuff. It's a fairly general subgrouping I know - that's what the internet is for isn't it?
Firstly, the W3Schools site has saved me from certain doom many, many times in the past. If you want to know anything about HTML code or all the other, more complicated, stuff that works with HTML code, then this is basically the only site you need to go to.
It's basically a site of tutorials on how to do stuff. All sorts of stuff. I'm not so hot at HTML, so I've used this site off and on for a while now - mostly to brush up when I've gotten rusty.There are step-by-step tutorials on how to do all sorts of things though. Things I've never even heard of before. It's a really well designed site too - easy to use.
The other site I'm going to talk about I've never actually used before Jason sent it to me in an email. MetaCritic is basically a reviews site that reviews everything - books, music, movies, DVDs, everything! Looking over their 'MetaScore' FAQ it looks like they don't actually have reviewers of their own, but that the site acts like a review-collector - compiling reviews from a number of sources. The only other site that I can think of which does a similar thing is rottentomatoes.com, but Rottentomatoes only reviews movies.
(EDIT 18/Mar/08: Fancy that, Wikipedia actually compares MetaCritic with Rottentomates as well. According to Wikipedia, MetaCritic mostly sources American critics, whereas Rottentomatoes mostly sources critics from the UK. This is an important difference because it often colours the reviews.)
Personally though, I don't think I'll use this site for my review needs. If you didn't have a good source for reviews, I think the multi-review aspect would be a great bonus. However I think that it could never be as good as one or two review sources that you personally find you really trust. For movies I use good ol' Margaret and David. They're not as snobby as you might think. With Margaret and David you don't just get the star rating (anything above 3/5 is worth seeing) but you also get their thought on why they thought it was good or not. That way I can still figure out if I'll hate a movie they said they loved, because of the reasons they give. I don't think you can ever get that with a huge multi-review site like MetaCritic.