this one lets one search one torrent spot to start but then keeps a toolbar search to let you go to about 10 of them.
(it does not install or load a toolbar, it's just part of the search engine)
http://www.torrents.to/
includes:
IsoHunt
The Pirate Bay
TorrentSpy
MiniNova
TorrentReactor
TorrentValley
btjunkie
TorrentBox
Demonoid
BiteNova
LiveTorrents
http://torrentsearcher.filesharingplace.com/
includes:
Bit Torrent
Box Torrents
Torrent Spy
BT Junkie
Download Anime
ISO Hunt
Mega Nova
Mininova
New Torrents
Seedler
The Pirate Bay
Torrent Box
Torrent Reactor