Are you sure no permanent mounting? That eliminates almost all the systems out there except for magnetic sound-hole pickups (the Baggs M1, Duncan MagMic, and Sunrise are all good) and the stick-on pickups like
the Schertler Dyn G (excellent sound but expensive and can feedback in high volume situations).
You could also look at something like the K&K Pure and Trinity systems with a Tapastring Vintage Jack...that won't require any drilling, but the K&K's work best when they are super-glued (rather than taped) underneath the bridge. Of course, you can remove the superglue but it can be a PITA. The K&K systems do sound very nice and natural but have a tendency to feedback at higher volumes.
My favorite system is the DTAR Multisource as it sounds almost as natural as the K&K and does not feedback even at high volumes. But it requires drilling a hole in the saddle to accommodate the undersaddle pickup, as well as enlarging the endpin hole to accommodate a 1/4-inch jack. The new-ish LR Baggs Anthem has also gotten excellent user reviews and would be worth a look, but like the DTAR it is going to require a small hole in the saddle for the UST and an enlarged endpin hole for the 1/4 jack.
Honestly, I think if you get a really good luthier who specializes more in acoustic guitars to do the install work, drilling a hole for a UST and enlarging the endpin hole are really not a big deal and will not decrease the value of your instrument. The only exception would be something like a vintage Martin...I wouldn't want to mess with that, but any modern instrument should be fine with a permanent install pickup provided it is installed by someone competent.