I use a Frigidaire 25 pint guy (had to go with the old school nobs instead of electronic start, because my atmosphere controller turns it on and off, and the newer electronic version needs to be manually restarted each time, as opposed to the knobs which restart as soon as power is "given" to them).
Honestly, though, any dehumidifier will do - the way they work is to suck water out of the air, which means that water in the "waste bucket" is pure as all hell (my R/O filter gets me 3PPM, the dehumidifier gets me 6PPM).
EDIT: But I'd go as big as you can afford - although my 25 pint works well inside my 4x4 tent, I'm going to get a really large one for the garage that it sits in (like 100 pints, if not more) because my 25 pint fills up so quickly - maybe I'll look to run a drain valve into my clean water reservoir, but I'd be scared to leave it for a few days if it was raining out.