I had a conversation similar to this a few nights ago. Are you looking to get started on kegging specifically *or* homebrew in general? Do you want to get into all-grain immediately, or stick with extract/extract+specialty grain? What size batches?
After your brew pot (go as big as you think you will need), a beginners setup is a beginners setup. You will find pros and cons for just about all the different types of equipment & materials used for that equipment, but in some cases the cheapest option is going to perform exactly the same as the pricier one (fermentation vessells specifically).
$500 is a bunch of cash, but when you start adding up the wish-list it can go quick:
$50-$100 for a basic stainless BK (5-10 gals)
$150-$250 for a basic kegging setup (single keg, 5 lb co2 tank, regulator assy, gas lines, beer lines, tap.)
$15-$40 for fermentation vessel (plastic bucket - glass Carboy)
$50-$100 for misc brewing equipment (airlocks, tubing, hydrometer, bottles, caps, cleaner/sanitizer, scale, thermometer)
$75- up for fermentation chamber with temperature controller
$20-$50 for your first recipe kit.
Plus extras that you will soon learn you just "have to have"!