I know others have already posted this one, but I wanted to put my two cents in. Scott Guthrie posted about the Patterns and Practices Guidance Explorer. The part that I thought was nice is that it comes in both desk top and web flavors. To some extent it seems to be little more than a dump of FXCop rules, but sometimes a search-able version of that is just what you need.
I think a good thing to do with this is to use its ability to add more items would be to include such jewels as those in “.NET Gotchas”. I would especially like to see more guidance around managing them memory footprint of applications.