70 litres is about 15 gallons so you need to be looking at only small gourami species. IMO, the best would be the honey gourami (Colisa chuna/sota). Note that a lot of other gouramies also have 'honey' in their common name so learn (or at least write down) the scientific name. A trio would work well - that is one male and two females. They are tricky to sex as juveniles. Males are generaly brighter than females with longer fins and a more streamlined appearance. Females are wider when viewed from above and deeper-bodied. If you find the wild type fish, females have a horizontal, dark stripe running from their eye to their tail and are a creamy brown. Males are usualy yellow-gold. When in breeding condition, both sexes brighten up a little but the males, especialy, develop a beautiful dark blue-black ventral area. I'll find some pics for you in a moment. Honeys are hardy and over-all peaceful though the male is territorial still. They like a planted tank with floating vegetation but you can sue fake plants just as well. They don't like strong currents (as with most gouramies) but are not picky in terms of food or water quality etc. Just as long as their tank is stable and they get a variety of foods, they're happy.
Dwarf gouramies are not a good choice for beginners. They are very highly prone to disease and easily stressed. They are also slightly larger than honeys (2" as opposed to the honeys' 1.5") and females can be tricky to find.
Many of the other gouramies sold in pet stores are good beginners' fish (eg: pearls and moonlights) but they grow too big for your tank. Do not, under any circumstances, allow an LFS worker to coax you into an impulse buy of a species you haven't researched.
The question of whether your tank contains fish is an important one. Also, if it doesn't contain fish, has it been cycled? If not, read the links in my signature about cycling and fishless cycling. You cannot cycle the tank with a gourami and small tanks are inherently difficult to cycle with fish anyway - fishless is always much quicker and less stressful - plus you aren't risking any lives! If you already have a tank set up, you also have the option of 'cloning' the existing one.
BTW - especialy to SugarQube - dwarf gouramies are actualy quite peaceful fish but shouldn't be kept in pairs. I say this all the time lol
They need to be kept as trios (like guppies) or singly (if male). Also, tank size and tankmates go a long way in affecting behaviour and unsuitable conditions often trigger violent responses.
Here's a pic of a male and female honey:
http
/www.aquariumarticles.com/articles/1236441/c_chuna.jpg (note that there are many color morphs and some are not as red as this).
/www.aquariumarticles.com/articles/1236441/c_chuna.jpg
