I get so many questions about what hardware I use that I decided to write a short blog entry that I can direct people to rather than giving them Steve Jobs style minimal answers.
I use a Mac Pro as my main machine, and currently have 2 intel i7-980x based render slaves. The Mac Pro is about 5 years old and boots directly into windows, in fact I can't even boot into osx anymore as I stuck a non osx verified graphics card in it. Bootcamp works perfectly with windows. Essentially all bootcamp is anyway is a set of drivers for the graphics card, audio, bluetooth, wifi, lan etc.
After 5 years of working for myself I have come to the conclusion that what is most valuable to me in my main workstation is reliability. My ageing Mac Pro has been incredible in this regard and if I replace it I'll probably go for a similar type of machine. So even though it might be better value for money to get a couple of i7 machines and overclock them, I would prefer to go the non-overclocked xeon route, with lots of ECC ram. Having your own mini render farm is great, but often for quick test renders what you really want is a very powerful main machine. Thats my preference anyway.
If you are on a budget then of course a single processor machine will be a better bet, especially as you can stuff them full of ram these days. I'm not very up to date on what the latest and greatest is in cpu technology and even less so when it comes to graphics cards. The best I can do is send you over to 3datstech.com as Andy Lynn's amazon lists are pretty handy and fairly up to date.