My favourites are Altavista and Google.

Altavista is HUGE and you can do an images search as well (and audio and video), but you must 'understand' somewhat how Altavista works before you get relevant results. I use the Advanced Search many times.

Google is different from Altavista in more than one way: The most obvious difference is the fact that the site itself is much... cleaner
Searching with Google is a VERY fast way to search either AND best thing (IMO): the search results are automatically filtered so that you won't have double URLs and other inconveniences experienced with other search engines.

PS: I'm getting 99% of the traffic on EmuDreams from Google (Google.yahoo.com as well) so that's another reason I like this S.E.