Thudbuster?
 

http://www.performancebike.com/shop/...e.cfm?SKU=6313


This has got to be the dorkiest looking thing I've ever seen

It looks dorky but the device works. In fact, that's probably one of the few suspension seat posts that I'll recommend. It certainly should be used for those comfort bikes where the geometry keeps you sitting straight up all the time.

What does it look like with someone riding it?

Probably looks like you have an absent-minded proctologist....

I have one that I use at times (commuting), but the thing is a tank - I wouldnt consider it when mountain biking, but I ride at a hard clip and dont need the extra poundage.

I used one for XC mountain biking. It's is heavy but it works as advertized. I wouldn't suggest them for clydesdales. I'm one, and there are times when I get saddle bob just pedalling. I think it's only designed to handle people up to 200 or so lbs.

Yeah basically its the only suspension seatpost worth trying... have a friend that absolutely swears by his.