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.