Maylandis would certainly work, but are almost the same fish as the blue orchid. Another less aggressive peacock would work - something like a stuartgranti. Alternatively, you could do a couple types of mbuna. Yellow labs plus rusties would be pretty nice. Yo8u could probably squeeze in a third less aggressive type if you kept the other two groups reasonably-sized.
If you wanted to do Tangs, I think that most folks say that a 3' tank is too short for Cyprichromis. But I have my C. leptosoma Utinta in a 40 now and they're doing fine. They are one of the smaller varieties.
A lot of people of Paracyprichromis nigripinnis in a 40 breeder. The are technically a rock dweller, but sort of resemble that sardine body shape of cyps and are a bit more open water swimming than most fish normally considered rock dwellers.
I think that a pretty easy setup for a 40B would be two pairs of rock dwellers plus a groups of shellies. Something like a smaller Julidochromis, a pair of comps/calvus and the shellies (occes, multis, brevis).
Besides buying a pair of adult fish, the general strategy is to get 6 or so juvies and let them grow up and pair off. When you get the pair, sell off/trade the rest of them.
