I like ISM and OSM and I find them attractive, especially as they approach 22. You get 100 or so BP of extra spread over TIPS for exposure to an A-rated credit and the bonds often trade down when it seems like they shouldn't (translation: illiquidity sometimes gives you a bargain). At maturity, you do indeed get $25 back.
These things are more akin to an I bond than TIPS, though. They also have an advantage over TIPS in that you get your inflation adjustment every month as cash on the barrel head, so if we subsequently enter a period of deflation (highly unlikely, IMO) you won't get the deflation taken out of your principal.
The best free source for info on ISM, OSM and other retail income securities that I know of is
www.quantumonline.com I think they will make you register, but since I am registered as "Heywood Jahblowme", I think it is pretty informal.
As these things head for 22, I am increasingly interested in adding to my position. A nice, low risk play, IMO.