On Cliki.net, there is a collection of Common Lisp Utilities, things that everybody writes since they're not part of the official standard. There are some very useful things there; the only problems are that they aren't implemented as well as you'd like (some aren't implemented at all) and they aren't conveniently packaged and maintained. It takes quite a bit of work to carefully implement utilities for common use, commented and documented, with error checking placed everywhere some dumb user might make a mistake.
The CLRFI process is a lot better thought out, and will probably produce better standards than informal discussion on a Wiki, but it has one problem: at the time of this writing, it's not doing anything yet. Until the CLRFI process gets going, I think that a high-quality collection of the informal standards on Cliki is a valuable thing to have. It's here, and it's called cl-utilities.