I would and I have, but I'm not particularly interested in doing so. nWoD is somewhat attractive these days, though, especially now that Werewolf is out. The Lord of the Rings (CODA system) is enticing as well, and I'd probably go for a run of some old MegaTraveller or Cthulhu (BRP, although here I'd definately prefer the d20 version) as well. I'd play some WFRP now that the new edition is out, if I could get anyone to play with me.
I'd also love to play me some Conan (Mongoose) or Mutants & Masterminds too, but those are only non-d20 by a technicality.
I've got plenty of non-D&D d20 games I'm interested in playing still, though -- Star Wars, d20 Modern, Wheel of Time, Cthulhu, Black Company and others have had very little play in my groups.