Carnival glass is a very popular item with collectors. The bright, irridescent colors coupled with a wide variety of patterns results in a broad range of choices and price points for both the serious and casual collector.
The brilliant irridescence of this type of glass was cutting-edge technology at the turn of the last century. Tiffany, Steuben and Loetz made gorgeous pieces of art glass that only the wealthy could afford. Development of an irridescent spray meant that cheaper glass could be made for the less affluent. This mass-produced iridized glass would later become known as carnival glass, when, after the Art Nouveau era it fell out of favor and surplus items were offered as carnival prizes and grocery premiums.
Several Ohio Valley glassmaking firms produced carnival glass, including Northwood, Imperial, and Fenton. Today you might be lucky enough to find some at a yard sale in the Cincinnati area, but it probably won't be cheap.
Once again, to get an idea of what carnival glass is popular these days, type the search term into the eBay search engine and see what comes up. Also check out the various collectors web sites:
http://www.ddoty.com/newcomers.html David Doty's Carnival Glass Field Guide
http://www.carnivalglass.org.au/What%20is%20CG.htm Australian Carnival Glass Collectors Association
http://carnivalglass101.carnivalheaven.com/index.htm Carnival Glass 101