Northernlight.com is THE biggest search engine out there at the moment, and it's collection routines for pages is excellent. Other such as Yahoo are by submission to their database only, they do NOT scan the internet. Alot of the other engines also can not handle sites that use frames to display content, this eliminates a large chunk of the net.
Northernlight is the one to use at the moment, for other junkies that want more . . . get a copy of Webbandit, this takes much longer to scan but will scan the net for you online, very useful for hard to find stuff.