The new Cateye V2c is what I would recommend. Only caveat is that it's a little pricey, and I don't know what your budget is. I just received one as a birthday gift to replace the wired Cateye Strata Cadence that had corroded.
Things I really like:
3 line display, so I can see speed, cadence, and distance w/o pushing buttons
Cadence
Rear-wheel pickup for speed, so still works on the trainer
Stores average and max speed/cadence info.
(Lap feature is nice to have, but more complicated than I care to deal with on a daily basis.)
Still fairly slim unit, and easy to mount
Wireless -- no external contacts to corrode from all the hours on the trainer
Only cons:
a bit pricey
buttons are a little stiff to push
slight delay (couple secs) for cadence changes. Doesn't really bother me. Speed changes seem to pick up faster