Way, way too much to list all of it. Some classics:
My entire Oly camera rig and housing. Bout the strobe and handles from Yuzo - got the cam and stuff from eBay. Sold it 8 months later for more than I paid for it.
My BP/W rig. Both of our canister lights. Both our Vytecs. Both of our Atomic B1 reg rigs (in 2000... still perfect.) All of my PST cylinders. All of our fins, gloves, hoods, and masks. Our Stahlsac dive bags, our SK7 compass' and my DIR Hose kit. Last week I just bought my new drysuit on eBay (NEW stock medium CLX450, with the zip seal upgrade to neck and wrists, new-in-the box rock boots, uncut zip seals, bag, talc, wax, etc, etc... for $750 delivered) and my currently too large, very good condition FLX50/50 signature series will be listed there this weekend.
My best deal was a mis-listed Diving Unlimted International dry suit. It was a custom cut (that would never fit me) that I picked up with 400 thinsulate and booties for $475 - and sold 10 days later for $1260. I've picked up a few canister lights and flipped them, flipped a couple of backplates, and will be flipping some other stuff this weekend I picked up last week on the cheap.
Its the greatest thing to ever happen to the internet, EBay. Since 1999 I have thousands of transactions and have made and sold many tens-of-thousands of dollars. Nothing like it. Its changed the way I live. If you're not going to eBay before you step out the door to go buy anything, you're burning your cash.
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Ken