I have yet to buy a saddle for it. I'm currently using the saddle off my road bike. It looks like this:
The frame is not as compact as a track bike (note the distance between the rear wheel and seat tube) and it's a bit goofy since I have 700c wheels in a frame built for 27 inchers, but I love it regardless.
It has Miche Primato hubs on Mavic Open Pro rims, Profile bars, OldSkool Dia Compe front brake with aero brake lever, euro asia imports cog, Pazzaz stem. The frame is an old Nishiki, circa 1970. The cranks and chainring are off an old Fuji Royale.
The gearing is a bit low (42x18) and I plan on going to a 16T cog when I get sick of spinning out on the flats/downhills. It's extremely quiet and smooth, fairly light (19 lbs or so) and the steel frame absorbs all the bumps and vibrations nicely. I wanted to keep the oldskool look and kept the chrome on the fork. I actually scraped the paint about 3 more inches up the fork, until the chrome ended.
There are more pictures here:
The bike was essentially built from the frame, minus the wheels, which I had laced, trued, etc. by an expert at the LBS. I threw away all of the old parts (except headset), sanded the frame down and painted it, and then installed the new parts.