I just published one of my holiday pet projects on Codeplex. It's a very basic framework for building your own card games in .net.
With time, I'll also publish some sample projects, and hopefully even expand the project to include some basic AI logic as well.
Check it out: http://www.codeplex.com/CardGameLib
Even though it's still missing a lot of parts, I've already begun to use it for 2 other pet projects. One is a code competition I plan to put out soon - just looking for price-sponsors now, the other is a web-edition of the classic 500-Rummy card game, a game that I really enjoyed growing up - and still play when I'm vacationing with my family. Card games are an excellent form of entertainment - and remember, there's more than poker and blackjack to life.
Drop me a line - or leave a comment, if you want to contribute to the project, sponsor a price for the upcoming code-competition or just have an opinion to share :-)