What Website Do You Use for Airline Travel?

I haven't flown in a couple of years and would like to know the websites that are used for leisurely airline travel. I'm flying from Phoenix AZ. to Providence R.I. the end of July. I heard that Tues and Wed are the best travel days so I plan to leave and return on one of those days so I'll be gone about a week. Thanks for any help.

Suggestion:

skyscanner.net over here in Europe.