There are a variety of web sites that purport to offer reusable code in some fashion (Krugle, Koders, byteMyCode, et al). These are great for browsing and for learning by reading other people's code, though I find it challenging to actually find something specific.
With O'Reilly's cookbook series (Perl Cookbook, Ruby Cookbook, C# Cookbook, etc.), on the other hand, it is quite easy to find a specific item. These books are well organized and quite useful.
What I am wondering (specifically for C#) is if there is some web site that takes the elegance of these cookbooks and makes them dynamic--that is, an easy-to-search collection of recipes that can be added to, or commented upon, by any interested reader? My current best available resource for this, ironically, is Stack Overflow itself. But SO only provides recipes that someone has asked for; it is not designed for one to just post an unsolicited recipe.