Depends on how much force you need; you'll have to figure that out.
There are continuous-rotation servos with lots of torque, like this one: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=130
15 Kg-cm means with a 2 cm diameter spool you could winch up 15 KG!! OK, you don't need that much.
A mechanical configuration I really like is the parallel-arm linkage that's shown on this robot which one of my kids built about 10 years ago. (I can hear it begging for an Arduino Reincarnation!)..
This used a floppy drive stepper as the winch motor, and it had a lot less torque than many servos...
...just throwing out ideas...
Anyone seen a Bot with that configuration? I thought he had a really cool idea back then, even if he was MY kid