Well regardless of exactly which species you end up with, it has to be kept as a school of at least 6. The more you have, the less shy and the more impressive. If you go for the angels, you also need to make sure the species you choose isn't too small or it may get eaten. Also be aware that some species are brackish, some can cause big problems when it comes to plants and some do nip if not kept in a large enough group so that they occupy each other instead. One last thing to consider is that some species might hybridize and that this isn't something that should be encouraged. It shouldn't be an issue in a community setting but please don't attempt to purposefuly breed 2 sepperate species with each other.
I've linked to a rainbowfish site with lots of beautiful pictures on various species below. The first link will take you to the melanotaenia sp. section, the second to the glossolepis sp. section. Scroll down the right side where the list of species are to find the particular fish I've mentioned or to take a look at various other possibilities. There are just so many rainbowfish out there. You could probably set up an all-rainbow tank and you'd have all the color and activity you need with just them.
Because you have the luxury of having a large tank, I'd reccomend a group of boesemani rainbows AND a group of turqoise rainbows. These have always been my to favourite rainbow species. The scientific names are melanotaenia boesmani and melanotaenia lacustris respectively. Both of these get to 4" and are peaceful but active and have stunning colors (purple and yellow/orange for the boesmani, bright turqoise blue for m. lacustris). They don't usualy cause much trouble when it comes to plants though they might nibble on a few. The other plus side is that, though like other rainbows the males are the most colorful, the females also have attractive coloring. Both are also generaly quite easy to get hold of.
http
/members.optushome.com.au/chelmon/Melanotaenia.htm
The smaller praecox rainbow (about 2") is also quite beautiful with a blue and red color. However, they can be quite nippy if not kept in a big group. Keep at least 7 if you want them in with angels or any of the long-finned gourami species (such as pearls). They are melanotaenia praecox if you want to look them up and are often found under the name blue/neon dwarf rainbow in LFSs.
Lastly, glossolepis incisus, the red rainbow, is a bright solid red color. It can get to about 5" so is the largest of those I've mentioned. I've never taken a particular liking to them like I have to the boesmani and m. lacustris but they are worth keeping if only for their color.
http/members.optushome.com.au/chelmon/Glossolepis.htm
