On most DECENT airlines (United, Continental, Air Canada, etc) the in-flight entertainment was more than enough to keep me busy. Little Space Invaders knock off built into the seatback, 4-5 different movies, some awesome retro cartoon playing, like Looney Tunes or Tom & Jerry, and I remember when I used to fly to Tel Aviv with Continental they had a channel that was allllllll CSI, like 8 episodes that looped. Well, now flying to Amman with *shudder* Royal Jordanian, you're lucky if you can actually SEE the fvcking movie (the entire coach cabin has a PROJECTOR playing the movie for them), and I keep myself busy with my Shure E2Cs and either my iPod, DS, or laptop on the other end.
Talking to the people next to you can be pretty entertaining too, last year I was sitting next to, *fanfare*, a U2 fan, a hot U2 fan, probably said so because of the U2 iPod I had. This year was slightly more entertaining, I got to sit next to one kickass drunk. He kept mumbling to himself about crying children, complimenting the hawt Asian flight attendant, and asking me what I thought about things in the paper.
If all else fails, just sleep.
EDIT: Damn Brits, I actually typed stewardess