Well, the name I miss the most I lost because my brother was the registrant (I didn't have a credit card) and didn't tell me he couldn't afford to renew the name. Yes, it's Crooky.com, and the asshole squatting on it now wants $4,950 for it. I've got the .net but it's just not the same. Ugh.
As far as names I regrettably undersold, there's a couple...I sold PayStars.com for only $1,500 (wound up being to a company who looks like they could pay more than that) and while I sold SexVideo.tv for a nice $1,200 at the time it was getting about 30 uniques a day with 50% clickthrough on Sedo, which, if I had known of Fabulous at the time and those stats translated well to Fabulous, probably would have made about $7 - $10 a day there as opposed to the 60 cents a day on Sedo. Also IMO undersold Poker.md at $2,000 last year too, as well as Ringtone.cc for only $650. There's a lot of names I miss.