I have a pair of Beyer DT880s that sound really nice and detailed, very comfortable to wear. They are not budget headphones, but they sound very good and seem to have a fairly flat, neutral response. Mine are open headphones, which tend to sound better than closed ones, but don't isolate noise (in or out). That means if you're monitoring instruments while putting down a vocal track, the vocal mike will pick up the headphones if you are cranking the music. And, if you're cranking it, other people can hear what you're hearing, too. They are usually in the $300 range.
If money's an issue, you can get a new pair of Sennheiser HD280s for about $70 or so, they sound good, not nearly as comfortable (they grip your head like you wouldn't believe) but good low end and decent highs. They are closed headphones. They were about $250 a pair when they first came out, as I recall.
You want to stay away from things like Bose, they have an artificially extended bass response to appeal to the iPod crowd. (I tried a $100 pair as a second pair of studio headphones, but the response was anything but flat.) And pretty much any name-brand headphone for short money, the Sennheisers aside, will sound like crap. There's no such thing as a good $50 pair of headphones once you've listened to the offerings out there at $300 and above.
I really like my Beyers. The "pro" version is a bit more, but the non-pro version sounds very good.
