I did a quick hack on hl-line.el today, inspired by this c.l.l post by Kent Pitman. hl-sexp.el emphasizes the sexp that point is in, and so far is surprisingly pleasant to use, even though the code frobs {pre,post}-command-hook to do its dirty work.

Grab it here.

Speaking of Kent Pitman, he just webbed an article he wrote on condition handling for Advances in Exception Handling Techniques. He rules.