Hi, Tom - and welcome to Reef2Reef!
For a tank like that, you've got plenty of options, from smaller tangs to gobies, from zoanthids to Acropora. What kind of lighting and flow are you planning on? That'll help to define the types of corals that might thrive there, and which fish will be happy.
I happen to like more, smaller fish in a tank, by and large - but I also enjoy having some of the taller "billboard" fish, such as angelfish and tangs - the iconic fish that just shout "reef".
A few favorites:
Shrimp gobies; several different varieties, sizes and price ranges, from hi-fin red-banded gobies and yellow watchmen to pink-striped aurora gobies, these guys will often pair up with a pistol shrimp to display a charming partnership.
Neon gobies and their kin; tiny analogues of the Pacific's cleaner wrasses, these guys usually do well in aquariums, and will solicit other fish to be cleaned of parasites. (They _don't_ eat ich, and can die from it just as easily as any other fish - quarantine everybody!)
Blennies; Tailspot, orange-spot, starry or lawnmower blennies (there are more, _lots_ more!) will perch on the rocks, watching the world with a curious gaze. When they're hungry and motivated, they'll help clear up your algae. Midas blennies have the same comically curious look to their faces, but spend their time up in the water column, snatching passing plankton. Or flakes. Whatever.
Clownfish; (Nemo!) As tough as they come, most are jerks, but some are worse jerks than others. Ocellaris, percula and skunk clowns are generally pretty tolerable; tomatoes, clarkii and maroons can limit who lives next door.
Other damselfish; (Clownfish are a subset of damsels) Some are holy terrors, but some of the Chromis and Chrysiptera families can be spunky, sparky additions to a big tank. I have azures and Talbott's, and have had no trouble with either.
Royal grammas; these little sea-basses can be hermits, but as they gain confidence, they'll prowl close to the rockwork, glowing in magenta and yellow. If you acquire them small and simultaneously, they can form "harem" groups, a single male with one or more females. Don't worry if you spot them swimming upside-down under a rock, it's pretty normal for them.
Dartfish; they're cute, but the smaller ones (lookin' at you, firefish) won't tolerate others of their kind, except their chosen mate. Zebra darts and blue gudgeons will shoal below the surface, waiting for tasty morsels. These guys can _jump_. Make sure you've got a lid of some sort!
Tangs; exercise caution - these fish like to _move_. A smaller tang such as a kole or yellow will be happy, a regal blue, vlamingii, naso or sailfin may not have room to turn around when they grow up, and if a powderblue decides the space is to small, ain't _nobody_ gonna be happy. They'll be happy to help with algae, but may view blennies as competition to be driven away.
Wrasses; fairy and flasher wrasses will glide effortlessly above your rockwork in search of planktonic snacks. (Some fairies are more compatible than others, Evolved has an _excellent_ article and compatibility chart for the group, up in the "Articles" section.) Leopard wrasses and members of the Halichoeres genus will patrol closer to the rocks as a general rule, picking pests and 'pods. Some shrimp or other invertebrates may be in danger from larger members of the family, but you may find the risk worthwhile. If there's any group of fish more likely to jump than dartfish, it's probably wrasses.
Angelfish; some love 'em, some ... not so much. Most angels can pick on coral, some folks insist that they all will eventually, save a single genus. (Of the dwarf angels, most folks report success with flames and coral beauties, of the larger angels, regals get the nod - though they're considered a challenging fish to get started.) Angels of the genus Genicanthus are specialized plankton feeders, and there are few fish more beautiful than a female G. bellus or a Watanabe's angel. Being plankton feeders means they're unlikely to make your corals into hors'doeuvres.
There are an awful lot of fish I'm leaving out, and some of them are awesome - but the list above may offer a few hours diversion. Scroll through the listings at LiveAquaria. Their info is pretty good, regarding the size the fish grow to, the size of the tank they might be considered for, what they eat and who they may not get along with.
~Bruce
