Some very good points here, and I definitely agree with the suggestions to spend some good money on the monitor/LCD - that's not a good place to go cheap. I got a deal on a 1680x1250 for $145 - but it's missing features that a better quality monitor would have, and I do find myself wishing for them more than once in a while.
As far as the power supply goes, I've got an 850W, but I spent extra to ensure that it was "green" power, energy star, and had the highest efficiency rating I could get. Yes, it's more than I need, but it's good quality and will last at least through 1 or 2 more re-builds (5-7 years) which is important to me; plus I use my comp for gaming a lot, and I wanted to ensure that notoriously voltage sensitive graphics cards and other high performance components did not lack in any way for stable, efficient power.
If you don't game (much) or plan on stuffing your computer with high perf. parts anytime soon, just get your hands on a good quality power supply of less than 600W and you'll be just fine. One key point is that if you plan on upgrading your system by adding extra hard drives, going with SLi or CrossFire, or anything else that requires more or specialized power connectors - make sure you get enough for what you might want. I've had to spend money on returns or buying new power supplies because it was short an adapter or plug, and that's pretty frustrating.
Just my $.02





