I got my kegging stuff from another homebrewer. My 3 keg system cost me $215 in the end. For a two keg system you will want:
5lb, 10lb, or 20lb CO2 tank (5lb should last 6-8 kegs, so you decide)
single or dual gauge regulator (I have a single, dual will give you line and tank pressure vs. Just line pressure)
splitter (get a three or four way and just leave two closed)
2x 5' gas lines (can get more later)
2x gas in couplers (ball or pin lock, depends on keg type on kegs)
2x corney kegs (I suggest ball lock because they have manual pressure release valves)
2x liquid out couplers (ball or pin, depends on keg type)
2x 7' liquid lines (use thick walled liquid line, 7' is just a suggested length many use 5')
2x shank/tap/faucet combo or picnic taps (perlick 525 SS or 575 SS are preferred, length of shank depends on fridge wall thickness, I use picnic taps soni have to open the door to get beer)
drip tray (if you do through the door faucets)
star-San or idofur sanitizer (do not use bleach or C-brite on kegs!)
misc length small brushes (for getting inside your dip tubes and faucets, look at one of the sellers mentioned to get the info)
I suggest all your connectors be "screw type" as apposed to barb type so you can swap things quickly.
you can either order all the parts online, or get them of other members on HBT or get them from craigslist or your LHBS.
I got the majority of my stuff from a member on HBT, some additional lines and couplers from my LHBS, and two additional kegs off craigslist.
To clarify - my three keg setup cost was
$150 (HBT member) everything for two keg setup 1 picnic 1 shank/faucet, expandable to three kegs
$35 (LHBS) for two picnic lines, extra set of in/out couplers
$30 (CL) third keg
=$215
I'm hopefully picking up another keg this weekend for $30, so I have a spare, that's why it isn't included in my overall cost yet.
All of my kegs are ball lock with pressure release.
Hope that all helps.
Edit: the reason I suggested to get the 3/4 way splitter is that eventually you will probably want more on tap, you may one across a great deal on some kegs or something in the future, and the cost difference isn't that much.