Memoflex Gel seat cover.

The seat on my mountain bike is not very comfortable (but it is pretty light in weight). Some folks I let ride really complain about the lack of comfort. Since weight doesn't matter on a stationary bike, I purchased a rather heavy PAINRELIEVER Gel Saddle Pad.
I purchased it from a local bike shop in Smithtown NY for $25 plus tax. It installs right over the existing seat and is held in place with a nice draw string and clamp. Install or removal is very easy.
I purchased the Regular size, although it's offered in Large and X-Large sizes as well. :
http://tricosports.com/painreliever_pad.html
Label on back of package:
Trico sports, Inc.
11-101
PAINRELIEVER Gel Pad

Y11-09-25