>>30
besides
copy-tree and the like,
subst/-if/-if-not and related, do let you map over a tree and replace elements selectively.
Mind explaining what kind of functions you'd like to see? Most of the times I needed to work with complex circular lists, I was dealing with graphs and more complex structures, and for those, I needed a full-fledged graph manipulation library (which I did find, altough, the documentation sucked, but was overall easy to use).