The big three are really it...Ask is 4th, but still a tiny percentage of overall internet marketshare. The big 3 are the only search engines to worry about.
If you get ranked well on yahoo ask lists site for free and lists it high. It is hard to get site ranked in all 3. If you rank well in google usually you do not rank well in yahoo.
The others will find you. It may be better to concentrate on getting listed on heavy traffic directories. Google, Yahoo, and MSN, in todays age, are the GM, Ford, and Chrysler from the 70's.
Not much, unless you count the metacrawalers such as Dogpile and Metacrawler too. I think exactseek had a rising search share too last time I heard, but still pathetically small compared to the big 3 engines.
Don't forget niche search engines! For instance, if you have a blog, make sure it's pinging Technorati and all of the other blog search services, if you run a forum, make sure it's indexed by BoardTracker, if you have adult sites, ensure they're spidered by EveKnows, etc. The volume of niche engines isn't close to the big 3, but they will provide some highly targeted traffic. If you've setup highly relevant text/banner ads, it should convert well for you.
I've recently been looking for the same info, a few notables are: A9.com Gigablast.com Snap.com Gigablast (I believe) maintains their own index, A9 is owned by amazon and derives its results from...I don't know, and snap is a meta engine pulling from several search engines and provides a snappy interface Happy Hunting!
Is www.jayde.com/ one? I have submitted my site there, but is it just like Dogpile and gets sites from Google etc?