Scieneer Common Lisp is now available in a free-for-noncommercial-use edition. Douglas Crosher did a lot of work on CMUCL in the late 90s, and Scieneer CL is his fork of CMUCL with a number of proprietary improvements to things like threading and networking. To get the free version you have to jump through a number of hoops like registering (which appears to be personally approved on a case-by-case basis) and creating a license file that is tied to the installation computer via its MAC address. I also got confused by the download page and accidentally got the 32-bit version; take a close look at the page layout before downloading. Scieneer CL has an interesting feature set and pricing looks pretty reasonable. I think the free download will be a decent way for potential customers to try-before-you-buy, and for library authors to avoid gratuitous incompatibility with Scieneer CL.
LispWorks is running a 50/50 special offer to celebrate Lisp's 50th birthday. I like LispWorks, but the 50% discount applies only to the 32-bit LispWorks Professional product, and I don't have any 32-bit systems any more (who does?).