I like to have 3 or 4 different reverb buses set up, sometimes even more. Remember you don't have to use all of them at any one time and you can even automate certain instruments in and out of the reverb - you can create quite a startling, dynamic effect by having an instrument reverbed for one section of the song and then suddenly as dry as a bone for a different section so that it pops right out at you.
Types of reverb I like to have set up:
1) A large hall reverb for depth
2) A medium room or chamber reverb, sometimes just mixing a little into everything for "glue"
3) A short room or "ambiance" reverb, great when you want quite dry sounding drums but not
too dry
4) Some plates - sometimes both stereo and mono. I sometimes set up 3 mono plates - hard left, hard right and center.
Don't forget mono plates, great for guitar and vocals. Sometimes you don't want any stereo reverbs at all - they can after all create muddiness and clutter if used too much. An LCR mix with nothing but mono reverbs can sound really clean and tight. You don't have to have an instrument's reverb panned in the same position in the instrument - experiment with panning a left-panned instrument's reverb hard right, and vice versa.
I like to set up low pass and high pass filters on the reverb buses, before the signal hits the reverb. This is essential if you don't want your reverb muddying the mix too much or making sound too bright and shimmery. You can cut out quite a lot of the lows and highs for this purpose - I typically high pass as high as 500Hz, and low pass as low as 8-10kHz. Makes for a much cleaner mix. However, if I'm going for a deep hall reverb to give atmosphere to a solo synth part or something (like an intro or outro especially in ambient or "trip hop" styles), then I'll sometimes leave the lows in the reverb and just let it get as muddy as it wants.
Also remember that you can totally get away without using reverb at all, substituting a few well placed delays instead. Delays create the illusion of space with far less clutter than reverb.
Experiment with effects on your reverb too. If a reverb is clashing too much with other instruments, cut some frequencies out just like you'd do with normal frequency clashes. In the case of stereo reverbs, remember that you don't have to leave them at full width. Use a stereo narrowing tool (e.g. Channel Tools) to narrow the field so that your hard panned instruments sound clearer. Also think about using a stereo tool to take some of the center out to leave room for your central parts (vocal, kick, snare etc).
You can get quite creative with reverb - unless you're going for a live feel (e.g. classical/jazz etc) then you don't necessarily need to aim for an "all in the same room" effect. I guess the whole beauty of music production is that you have way more creative options for sound shaping than you do in a live setting - might as well make use of them. I've experimented with all sorts of stuff on reverb buses - adding distortion, flange, chorus, tremolo and hard compression. You can get some pretty interesting sounds!