This wiki page holds a list of pickups you can buy and put on your violins. Edit this page to include missing designs
Generic pickup from ebay
Barcus Berry 3100
Tested on an accustic violin by @guysoft review:
This pickup really sounds decent, and a major advantage is you can attach it to any block of wood with just two screws, making it easy to switch between prototypes.
Its shape makes it hold the bridge from moving too much, which is good, still picks up some ambient sound, but for its price its a decent pickup.
There are also V-100 and V-200
Schatten V-03 Series
The pickups on most of Wood violins.
Also has MIDI support