i7 920 is reasonable priced/competitive, especially if you find a nice motherboard/RAM combo
I recommend 6GB expandable to 8 or 12 if you want something that's going to last a long time and handle some serious multitasking.
Video cards are a dime a dozen and easy replaced, same with hard drives. Spend the bulk of your money on the cpu/motherboard/RAM (yes, you can upgrade RAM later but tech changes quickly and what is compatible now will probably not be on sale 3 years from now). Get a good quality power supply that fits your needs. I'd choose a 500W Thermaltake over a 900W no-name any day
Don't bother with SLI/Crossfire if you aren't a supergamer. You can't multi-monitor in those modes anyway!
Tom's is always the place to go for CPU benchmarks, Anandtech has good reviews on everything else.