A warranty deed is a particular type of deed which contains guarantee statements from the seller that the house will be transferred free of something which undesirable. Usually, that means it will be transferred free of any "liens and encumbrances" such as a federal tax lien or previous mortgage.
As a buyer of Real Estate, if you get a loan from a bank, they will absolutely demand a warranty deed as well as "title insurance". The insurance is a guarantee from a title company that if the house turns out to have a lien or encumbrance, the title company ill reimburse the buyer for any damages.
Conversely, a "quit-claim" deed is a deed which just transferrs the house complete with whatever liens or encumbrances which might "cloud the title". You'd issue a quit-claim deed to a buyer, for instance, if you were in bankruptcy and couldn't continue to make payments on the house. You just want out from under it and want to walk away. You'd be "quitting your claim" on the house.
Here's a little more reading info if you're interested:
http://en.wikipedia.org/wiki/Quit_claim_deed
Not sure if this one will come up (I just wrote it. They didn't have a warranty deed article)
http://en.wikipedia.org/wiki/Warranty_deed