I think two great options to look into are the Fostex T50RP's and the M-Audio Q40's. The Q40's are great headphones for bass without ending up with a recessed midrange. And they are only $99 on M-Audio's website. Don't be fooled by the price, though, because these are phenomenal cans. IMO, they are miles ahead of the DT770's with the exception of highs and soundstage.
The T50RP's would also be a great choice if you are interested in modding at all. I bought a pair and followed BlueMonkeyFlyer's thread for modding and I've ended up with an incredible pair of headphones. The frequency response is nearly flat and the characteristics of the planar magnetic driver make them very fast with great bass extension like the HE-400. The best part is, whenever you want to alter the sound a little, there are plenty of tuning techniques (i.e. more bass/less treble or less bass/more treble). I followed his DBV #3 tutorial and then altered it to have a slightly bassier sound. They are a great compliment to my HE-400's. If you aren't interested in modding, look into MrSpeakers' version of the T50RP known as the "Mad Dog". You can check them out (as well as their frequency response) on his website:
Thanks for posting this about the Fostex! I'll almost certainly have to get some and play around with the mods at some point. I'd been curious about the Mr. Speakers, or even the... Paradox I think it's called? But I think modding my own and the tweaking my own could be low cost fun and non-pressure way to hone some skills. I'm a little nervous about messing around with expensive cans since I'm not the most adept.