im no expert but i once had a craptastic power supply (my first computer) and then one day it exploded and fried my mobo, video card, and a hard drive. lost my whole computer and files in one fell swoop.
from that day foward i was an Antec man and they've never let me down. basically, dont get cheap on your power supply!!!
another tidbit, from an engineers perspective, usually power supplies come with an efficiency rating. if you leave your computer on a lot, spend a few extra bucks and get a high efficiency to save power. >70% efficiency is about average but i'm pretty sure there are models out there with closer to 80% efficiency. for the life of me i can't remember who makes them.
your computer's power supply uses almost as much power when its idle as it does when its under "full load" so that efficiency becomes important over time.