I use TorrentSurf.net, it is not a search engine of its own, but instead it searches on many search engines simultaneously.
Just type in something and it will search for the following torrent sites:
Mininova
The Pirate Bay
IsoHunt
FullDls
Monova
Fenopy
NewTorrents
BTjunkie
SeedPeer
TorrentHub
Demonoid
LegitTorrents
SumoTorrent
Mybittorrent