small preamps. half rack space, stomps etc

[dunamis]

This is good advice.

It'd be nice if there was a more consistent "industry standard" but, instead, output levels and input requirments are all over the map.

But I do have to say that it sounded like the OP was looking to provide a signal to the FOH, which is different than providing an input to a power amp.

One note I always have to interject: not all preamps can drive all power amps, in case that is one of the goals of the OP. If it is desired to drive a power amp, check the peak output voltage of the preamp and make sure it is an equal-or-larger number than the input sensitivity voltage rating of the power amp.