We're not selling them because we love them.

I have a 2004 GMC Yukon XL Denali that we bought 2 1/2 years ago with 70K miles for $17,000 with ALL the options (Nav, DVD, heated 2nd row Captains seats, etc.). It now has 130K miles on it and according to NADA Blue Book, it's still worth a little more than we paid for it, $17,300. We got a screaming deal obviously, but even with the gas prices, it'll be a cold day in you know where before I'll let go of it. With that said, we found ours at a dealer that listed it on autotrader.com and have found most of our used cars there, both privately and sold through dealers.
-Astrid
Edited to add: We went to look at a Volvo XC90 that my husband was considering trading in his Chevy HHR SS for, but we took my Denali to go look at it. The salesman was salivating when he saw my Denali thinking we were trading it in. He even tried to get us to trade it in by offering a lot of money for it and a really good deal on the XC90. We turned him down of course, but he said he could sell 10 of those a day. They do hold their value and ours has been trouble free except for routine maintenance so if you do find one for a good price, I'd jump on it.