Well that's what I'm looking for. I'm barely through the Guided Tour of McCLIM and some of the examples aren't working well and I have no idea what other toolkits there are and which are good. I would appreciate some experience reports and recommendations.
If you don't mind the spartan look and the lack of its own documentation, you can use ltk. It's quick, no-frills and very easy to use -- not to mention very straightforward if you used Tcl/Tk before. Some Tk functions are not implemented, but it works fairly well if you don't need anything serious. Otherwise, I'd recommend clg as well.
You can use lambda-gtk. The version on site is old and not working on sbcl, but it is trivial to get it working. It offers a complete gtk binding. (the patch to get it working is http://mo3r.nm.ru/lambda-gtk-0.1-sbcl-c ... -asd.patch ) Other gtk+ bindings didn't work for me (apart from cells-gtk, which I haven't tried).