I will be in Spain for a month in June, and will need to fly from Madrid to Venice and then from Udine, Italy back to Madrid a week later. Any suggestions for airlines, and should I book the flight here in the USA, or just wait until I am in Spain?
Vueling is a low cost carrier out of Spain that can get you back and forth from Madrid.
Another option is to look at www.sidestep.com - it will do a multi-sight search for you of carriers and prices.
And don't wait until you get to Spain. Discount tickets go quickly, so snap them up on the web as soon as you find a carrier that fits the bill. BTW, Vueling's a great little airline...new planes, friendly staff.
Use these search engines to find which, if any, budget airlines fly your routes: www.whichbudget.com and www.skyscanner.net.