Here is a little infographic from testking.com – I would have placed the whole graphic here, but it is a little wide for my site, and besides they deserve the traffic for the work.
I feel like I spend hours arguing for and against certain font choices based on rather ancient stats on what computers have what fonts. I tend to be a minimalist, Arial, Helvetica, Times [New Roman], but with this I might be able to expand a little bit on that beaten path.
Unrelated: I have been working on a site that utilizes fonts from webfonts.fonts.com, which has been pretty interesting. There have been some quirks, formatting and style issues, but in general it has been working out pretty well. If you don’t have much traffic, they have a free service which is useful for testing. For you designer types I would recommend a look at it – it will slow you pages down a little, but overall we have been very happy. I will have a better idea about cost once we launch and are out of beta testing.