I hope you were joking on the "time is not valuable" thing, OperaDad. I'm in graduate school in New York, and no way I want to be traveling from the airport at 11 at night. LOL! I travel relatively often because I go to conferences to present my research and to special training opportunities for grad students.
AirTran has a special deal for people ages 18 to 23 that allows them to buy one-way stand-by tickets for $79 (+ fees/taxes). I don't remember the new name of the program -- it used to be called X-fares -- but it is standby flying, which means that you have to go to the airport and buy the tickets at the counter, and you're not guaranteed a space on the flight. However, I've used it a couple times and only once have I not made the flight I wanted, and in that case I was just bumped to the next flight out.
Everyone always raves to me about Southwest, but Southwest didn't service New York and won't until the end of this month, when they add service at LaGuardia airport. Same thing with JetBlue -- cheap flights, but it doesn't go to a lot of the cities conferences in my field are commonly held in and it doesn't go home. I use kayak.com and I find the cheapest flights that way -- recently booked a round-trip mid-afternoon flight to Toronto, flying out on a Sunday and coming back on a Sunday, for $187 (taxes and fees included). I also recommend lastminute.com if you need to make last-minute flight arrangements. An emergency happened and I had to fly home to Atlanta from New York, but I only found out about it the week of. I was able to book a round-trip flight AND a car AND a hotel for $250. I booked it on Thursday and left Friday!
I also agree with HImom's advice -- don't book flights until your dates are set. This includes finals times and spring break trips. Professors are notoriously steadfast about not allowing students to test early simply because they've already booked a flight home or to their spring break destination and don't want to pay the change fees (and anyway, it's rude to ask your professors to move up your finals dates because you want to start your vacation earlier). Also, like she says if you can help it, don't check any luggage. I pack all of the clothes I need for up to a week in my little rollaway carry-on, and then I pack my other things (like my computer and books) into my bookbag. Helps since the airlines are now charging you to check even one bag!