If you are using caliper brakes, you want standard-pull levers. If you are using V-brakes or disc brakes, you want levers that pull a longer amount of cable. Standard-pull mountain levers should work fine with calipers. Some levers are adjustable and can be used with either type of brake, you might want those, since if you change the brakes later on you won't need to change the levers.
For mountain levers, I have no particular recommendation, they seem like they are all the same. If you want to have indexed shifting, you might want to consider levers from Shimano or SRAM that have the shifters built in.
Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
I'm trying to envision what you are looking for but I suspect that Tektro cross levers are what you are looking for. They're less intrusive-looking than conventional brake levers and they come in 3 different clamp sizes so, if you get the right ones, they'll fit your handlebar for sure.
Most moustache handlebars (including the above posted Nashbar) take brake levers with a 15/16" (23.8mm) clamp. Most MTB and upright brake levers have a 7/8" (22.2mm) clamp.
If you want a MTB-style lever, you're best off with a cross top lever with 23.8mm clamp (as opposed to 26.0mm or 31.8mm) like Retro Grouch mentioned--these would normally be used as a second set of levers on the flat top portion of drop bars. (The other option is getting a MTB lever and honing out the clamp). The only good place on a moustache bar for these types of levers would be the ends. These levers angle away from the bar, whereas road/drop type levers angle toward the bar (to match the curvature).
I have moustache bars on my single-speed commuter and I spend most of the time in the hooks. The road/drop bar levers work well there. But if you'll be spending most of the time on the ends, then the cross levers would work well (might even want to flip the bars to get you even more upright).
Edit: Yes, these cross levers are compatible with standard road calipers.