Recently I mentioned the Quicklisp indexing site Quickdocs. Since then, Fukamachi has continued to improve the site. He's added categories so that you can browse the list of all libraries concerned with, say, Graphics. That gives you an idea of what's available and, of course, you can drill down into any package that looks promising.
The site is generated automatically whenever a new Quicklisp distribution is released so it's always up to date. This is promising to be a really great resource. If you haven't taken a look at it yet or haven't seen it since it was upgraded, it's well worth your while to pay it a visit.