The planetology section of Orion's Arm might give you some ideas. I believe, too, that there are various programs out there that generate planetary systems with rules according to current ideas; this would not only make the system believable but automatically work out the various numbers (average temperature, year length...) for you.
Finally, you might want some really peculiar places. Neutron star planets, planets with more carbon than oxygen, planets of solid metal formed by blasting all the volatiles off a gas giant during a supernova...