I would not recommend buying a Mac - I bought one because that is the only way to develop for the iPhone/iPod Touch (still haven't gotten around too it). It is true Mac offers little options. Some Mac junkies like to argue that you get the best technology, and you get what you paid for - however, since you are on slashdot, chances are you will not like the 'dumbed-down' approach Mac OS X takes. As with desktops, the only upgrade path is buy a new Mac (unless you have a Mac Pro), limiting your opportunities to add a new video card, or maybe an additional hard drive, etc.
As for the original question, I use Newegg and tomshardware.com for all of my info, with the occasional google usage. I start with a motherboard I want, (taking note of northbridge), and look it up. I always pick Intel, they are much better bang for the buck than AMD atm. Processor wise - last time I made a computer it was all Core 2 Duo, with the option for extreme or not - much easier. But now you have i3, i5, i7 which are the lastest generation, on a LGA 1366 I believe, the i3 is the lowest tier, and i7 the hardcore enthusiast/gamer/video editor tier. I don't know anything about the models, just look for cache size and speed, those are the main specs for a processor. For the video card, I go with Nvidia because its much more compatible with linux (and FreeBSD) if you like to use their binaries vs. open source drivers. They recently changed how they do they naming, the lower 200 series, I believe are re-casts of the some of the 9xxx series.