POW'R for Safari 6.0
(Works on Apple's OS X 10.8 Mountain Lion and OS X 10.7 Lion when using Safari 6.)
We use (and love) Pow.cx
The integrated search in Safari 6 was really getting us down because it redirects '.dev' domains to search before Pow can get to them.
This extension prevents the auto-search in Safari 6 from automatically searching when it sees the '.dev' domain. Actually, if you go into settings you can specify a full list of domains you don't want Safari to accidentally search.
Shout at me on twitter (@agileanimal) if you are having an issue - but this is totally unsupported and comes without any warranty.