Ollo headphones are great.

I have the Beyerdynamic DT 990 Pro 250ohm. Think they were $150 when I got them and they are criminally good for that price-point. I own the Ollos as well and they are better - but they're like 5-10% better and over triple the price.
Your experience could vary but Beyerdynamics (with some room correction software) is the absolute best value per dollar I've spent on any music hardware.

I also have the DT 990 Pro and the Ollo's. I use them both, but not for my actual mixing. For that I use my speakers. I recently purchased ARC On-Ear, from IK Multimedia for my headphones. I works really nice with both of the headphones.

I can recomend you the sennheiser HD650. I also have the Beyerdinamics 990

I have the Sennheiser HD600. I think Beyerdynamic are more for tracking.

Sennheiser HD490s are pretty solid.

I can recommend the Sennheiser HD 660 S, definitely worth the price.

I would recommend Hifiman Ananda Nano IF you are going to EQ it (which i strongly recommend)
For around that price currently by far the best headphone if you ask me

You might want to look at the Ollo's and Slate. There are so many good ones. Sony also makes a damn good pair for the money.

In that price range, the Audio Technica ATH-M50x is a pretty good set of cans. The one thig that I recommend with these is changing the ear pads to the Dekoni Audio Velour Ear Pads. They give the M50x's an open back feel. They work well for me.