Portia, have you tried Ruby? That is another beautiful language (and no wonder as it has taken a lot from Lisp).
For Lisp experimentation purposes, Arc is really clean - it doesn't have the kind of cruft that CL has. However, if you are planning to implement a for production project in Lisp, from all I've read, Common Lisp is the way to go as it has a wide and mature range of libraries, which Arc presently does not. And among the CL dialects, SBCL would be a good pick. Be sure to use Zach Beane's QuickLisp utility to find and install CL libraries. IMHO.
You can always call Python from Arc to use some libraries.
A Python dict to s-exp converter is about 38 lines. There's a fromjson.arc (breaks over some input) and a tojson.arc (broken, creates an extra }) somewhere that could help talk to web services.
