One presentation that particularly gripped me was all about Deep Web - the places Google doesn't reach! From this, I found a number of useful sites, some of which I'd heard of before, but none of which I'd made anywhere near enough use of.
Here's a quick rundown:
www.picsearch.com - a database for finding images, seems more useful than Google Image Search
http://friskr.com - ditto the above
Meta search engines
www.dogpile.com - searches across Google, Yahoo, MSN and Ask all at once
http://clusty.com - A clustered search engine - it clusters the results it brings back by categories
www.mamma.com - similar to the above
Health meta search engines
www.medic8.com - can also browse index as well as search this one
www.webmd.com - health search engine
www.mammahealth.com - same stable as Mamma, but health related - seems very good indeed -try out the aspirin search!
Database search engines
www.completeplanet.com - searches for databases on a topic, and has a browse-able index
www.geniusfind.com - another index of databases categorised by topic.