Seymour Duncan SA-3XL Woody XL Series

With a bit of adjusting, this pickup is a great companion for an acoustic guitar. It has served me well throughout countless gigs as well as in the studio. The exposed pins make it easy to adjust the levels, so, though it was initially very trebbelly, I found the perfect mix fairly quickly. Bear in mind, it is a passive pickup, so it is not the loudest when it comes to bigger gigs, but for smaller venues and for rehearsals it is ideal. The cable is of good quality and sufficient length, and the soundhole fitting method makes it so easy to slide in and out of most guitars (I've even had to switch between guitars on stage with no fuss whatsoever).
I would highly recommend this product for those who can't afford a new semi-acoustic guitar but need the option of amping up for gigs. (It's also great fun to play with effects on an acoustic!)