How much space do you have? The larger the tank the larger the variety of fish you could keep. A 75 gallon would give you lots of flexibility, but a 55 could keep a decent number of smaller fish. Are you thinking singles of species or breeding pairs/groups (for some, this makes a huge difference...a paradise male paradisefish will create a large territory and vigorously defend the fry if there is a female to spawn with, but usually is fine as a single fish in a community - provided the community is a 20 long or more).
Glass cats, though, usually require food floating in the current, so they can be difficult to keep with piggy eaters. Harlequin rasboras would do great with most SE asian labyrinthfish. Dwarf chain loaches or kuhli loaches would also work well in a SE asian tank and be peaceful. Galaxy rasboras would also be nice in there either with or instead of glass cats.
If you want to have as peaceful a tank as possible, the smaller labyrinthfish are your best bet: honey gouramis, dwarf gouramis, croaking gouramis, a solo beta or female bettas, banded/thick lip gouramis, and maybe pearl gouramis as the big, but peaceful, centerpieces.
A more rough and tumble tank could include a short finned betta (the giant bettas at petco for example), a solitary male paradisefish, blue/gold/platinum gouramis, banded or thick lip gouramis (peaceful but large enough to hold their own), etc.
There are a host of more unsual gouramis that would fit in either tank. I'd start slowly and not overstock - plan for when they're adults. The smaller fish in a big tank will have many fewer conflicts...even if the 55 gallon.
Eric
