I got the 280 and they are great. You can get em refurb for about 65 bucks!! Even if that seems costly it will save you money in the long run as cheap headphones break frequently! Check it: Amazon.com: Buying Choices: Sennheiser HD-280 PRO Headphones
I've used mine daily for about 5 years now.
Admittedly they're starting to show signs of needing reupholstered but seriously...they've had some use.
If I can't get parts I'll definitely pick up a new pair. They're great.
If you need to really isolate the outside, and also have loud, decent sound in the cans....the studio veteran Koss Pro 4AA are the ticket. They clamp on solid and don't move with every tug of the headphone cable.
I use Sony MDR 7506's. Isolation seems average and I find them to be a little bright overall. They are super comfortable though and have extraordinary detail in the mids and highs. I think they're around 100 bucks?
Senn 280's have been a great addition for me, but only as far as monitoring post track. I have several pair though out my studio, but have found that they bleed a bit much when the gain is hot. The Sound Isolation Ex-29's are very much worth the couple extra dollars. My drummers and bassists swear by them due to their low end, but I have found that for very hot recordings, when the Ex-29's are in play there is far less clean up to do.