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You do not give your location in your profile, search engine popularity does have a lot of geographic variation.
In the US there are 2.1 search engines:
Google, which powers Yahoo!, AOL and many others. For me, and many others, it provides 80% of search engine referrals.
Inktomi, which powers MSN and will probably soon power Yahoo!
The 0.1 is Ask Jeeves.
Outside the US I believe that FAST has a substantial presence.
While I agree with most previous posts, mileage can vary according to location and language.
International English :
Google
Yahoo
MSN
Ask Jeeves
AOL
Lycos
Altavista
Local French Canada :
Google
Sympatico
La Toile du Québec
Yahoo
MSN
AOL
Altavista
Local English Canada :
Google
MSN
Yahoo
Sympatico
AOL
Ask
Altavista
<added>Mohamed_E beat me!</added>