I haven't heard of a compact for MTBs...

That said, I only use a double anyway. In most of our races/terrain here, there is no need for a "big ring". I find I can ride most anything, including a recent "dirt road crit" with just the double. This also provides more clearance for me with logs and rocks.

Like V said, think of the gears you will use. A triple is likely unnecessary (I take that back if you live in CA and are MTB riding in the hills!).

SheFly