Speaking of which - you mentioned a slot canyon in the Island district that is 4wd-accessible only - are there any that are reachable with 2wd?
There are no real ones in the park that can be reached with 2wd, but there are some "joint-like" slots in the Needles (or Arches too).
There are short slot canyon slot canyons around Moab, most of which can only be reached by using ropes, but slot canyon-wise they don't compare to some other areas on the Colorado Plateau (such as Robbers Roost, North Wash and Escalante) areas.
That said though, Onion Creek near Fisher Towers and north of Moab has some nice slot canyons. I have added them to SP since they are used to acess the climbing areas in the Fisher Towers, but they can be done in themselves if you want to see some slot canyons.
See the page below and the route pages attached:
http://www.summitpost.org/area/range/15 ... owers.html
The routes with the slot canyons are C1, C2, C3 and C4.