These threads get revived or created periodically. IF you want to try a set, suggest looking at the wheelchair tires (even have 700C [28-622] and 26x1" [20-559] sizes). They have inserts (tube replacement) as well as 'airless' tires and in some applications, different densities (what they call 60, 80, or 100 psi equivalent). For $20 on up, it's not that big of an investment and there's plenty of tread patterns, colors, and tire construction materials to choose from. If you need to do a return, the big Medical supply companies are a lot better to deal with.

Kenda offers inserts, if you want a brand name:
http://www.americanairless.com/airfree_innertubes.htm
I would use tubular glue though to keep the tire on the rim, esp critical for fast cornering.

Airfree tires and/or inserts will be heavier than any pneumatic tire/tube or tubeless combination. And as mentioned, mounting airless anything is a pain.