I'm looking for some last minutes deals out of YOW to southern USA (Florida, California, Texas) I'm looking a lot on hotwire and saw some good 350$ fares for next day departures. The Hotwire Limited rates are especially good!
Are there other sites that offer last minute airfares?
Priceline's name your own price or Lastminute.com's packages
You can get the lastminute.com packages on a bunch of sites -- most of the airlines have the same deals (same search engine), travelocity has it too. Sometimes travelocity has discount codes that make it cheaper, and TV allows you to have 2 people originiate in different cities. There are also cashback referral sites like ebates and fatwallet that give bonuses, I think travelocity has the best cashback.
Don't forget to look at packages that include both hotel and flights. Sometimes they are cheaper than just the airfare and there is nothing to prevent you from just not showing up at the hotel.
flight + car and car+ hotel options are also not bad. Look at everything, including doing flight +car for one person and flight + hotel for the other, espescially if you have a copon code you can use on each!