I mix in the cans, I know people are opposed to this but I've gotten some pretty good mixes. I was using some pretty good Sony cans, but recently got some Ultrasone Pro 900s. They sound "completely different" than the Sony's, really rich and deep bass. The impact on the sound while mixing is profound. I would like nice near fields, but I don't have that option right now. But I can't say enough about the Ultrasone Pro 900s, they rock pretty hard.

I use Beyer DT990, open back and very flat response.  It's **** that you can't pull good mixes from a pair of headphones.  It's just that you've got to know how to read meters properly and understand frequency response.  I recently finished a uni project all mixed in cans.  Went into studio to test mixes, perfect.  
 
Ben 

At the price that Ultrasone Pro 900's sell for, they had better rock hard!
Wow, those are some 'spensive headphones!
 

i've used the ultrasone pro 750's, they are really really nice..
 
but
 
you'll never get your mixes to truly translate properly across multiple playback systems using just cans.
 
just sayin

It depends a bit on what the end listener playback system is going to be.  If it's headphones then creating a mix on phones might work pretty well.  If its speakers then you should at least hear how your mix sounds on speakers before sending it off.  As Ben says if the phones are good enough then there is no reason why a great speaker mix cannot start on phones.
 
I used to have a pair of Stax SRX/ Mk III 's electrostatic headphones. Had a special driver box and they needed a high end power amp just to drive them!  In the 70's they were around $1000.  They are the closest thing I have heard compared to a high quality full range speaker.  It is like sitting right in front of a very good studio monitor.  I think it is easier listening to a great speaker mix on great headphones.  Harder trying to mix on phones and then hearing that on speakers.
 
You do have to make adjustments.  Reverb being one of them.  I tend to hear the reverbs very clearly on phones  (hence turning them down)  only to find things are a little dry on the speakers.  Panning is another area of concern.  Headphones accentuate panning so what may sound slightly panned in phones might appear more centre in the speakers.  And things that sound panned in speakers can sound extreme panned in the phones and so on. 
 
Keep your mixes fine tuned using buses and stems. Mixing at track level for balance but buses and stems can be trimmed easily.  eg reverbs turned up a little for speakers.  You could even use Channel Tools to alter the panning on a stem or buss depending on speaker or headphone listening.  It should be possible to get the two areas of speakers/phones satisfied.  When I compare mixes on the full speaker system compared to a mono Auratone type speaker at low volume, it is possible in various adjustments to satisfy both of those.  Likewise there must be middle ground for speaker/headphone approaches.  When several conditions are satisfied like that then translation works over many different playback systems.
 
I am interested in hearing how those special systems sound that make headphones sound like a pair of (various!) monitors in a room.  That could be well worth investigating.  Another area where I find headphones very useful is obviously working out of hours and keeping quiet but for detailed microscopic editing thay are very good indeed.  You can hear much more on phones when you start to go through parts in detail.
 
But for the OP the more money you throw at the headphones the better they are going to be and be tending towards nirvana.  (I could not believe how loud the Stax could go!)

Good point, reverb is essential, and probably the most challenging aspect without some air... I didn't think about that. If you work at it though, I think you can get some pretty darn good results without air? (holds breath until others agree.)

I think that as long as you know your monitoring environment, you can be fairly consistent, regardless of what you're using.

Mixing on cans..... yup, I've done it a time or two. I have some cheap ($30 bargain bin on sale) Yamaha cans.  But I never do the final mixes on cans...... without testing it and checking it on the monitors.
 
 
If you learn the cans and really have good ears I think it's possible to get a decent mix on cans. BUT.....as was pointed out, the cans you buy in the stores tend to have BIASED sound designed into them...... fat heavy bass, bumped mids..... all in the attempt to get a signature sound and make the music EAR CANDY to their customers.
 
In this business/hobby, we don't want "ear candy" in the studio. We want..... or hopefully so, the closest approximation to the actual truth in the music..... let the end user add the ear candy...we just want it to work on as many system/platforms as possible and sound good.

Good headphones are indispensable. Having more than one model is helpful, too. I'd be very frustrated if I had to mix without headphones.
 
In my experience, however, a good mix made entirely on headphones will not translate as well as a mix that was started on headphones and finished on speakers. That experience may not extend to everyone, though, especially those who are mixing in a poor acoustical environment. Unless you've invested in acoustical treatments and quality full-range speakers, you probably will do much better with high-end headphones. 
 
As for the Ultrasone 900, I'd love to have a pair as an alternate reference. But I wonder how they'd do as a primary reference as they're quite unlike anything else, whether you're talking cans or loudspeakers. They're extremely bass-hyped, on par with Beatz by Dre. OTOH, they have an extraordinarily flat (for headphones) and extended high end. They sound wonderful, especially if you like lots o' bass.
 
But I'm guessing a mix made entirely on them could likely end up sounding bass-light on a truly flat system. How about it John? Post your best mix made entirely on the Ultrasones and let us listen to it on a mix of speakers and headphones and report back.

Guitarhacker
Mixing on cans..... yup, I've done it a time or two. I have some cheap ($30 bargain bin on sale) Yamaha cans.  But I never do the final mixes on cans...... without testing it and checking it on the monitors.
 
 
If you learn the cans and really have good ears I think it's possible to get a decent mix on cans. BUT.....as was pointed out, the cans you buy in the stores tend to have BIASED sound designed into them...... fat heavy bass, bumped mids..... all in the attempt to get a signature sound and make the music EAR CANDY to their customers.
 
In this business/hobby, we don't want "ear candy" in the studio. We want..... or hopefully so, the closest approximation to the actual truth in the music..... let the end user add the ear candy...we just want it to work on as many system/platforms as possible and sound good.

Hence I suggested what I use DTT990's not the best but supposedly headphone monitors.
 
Ben