If you're just looking for ideas (you don't know where to start looking besides the really common names like the m50), there are at least a couple lists you can start with that feature quality reviews:
The over-ear and on-ear headphone head gear lists here:
and the InnerFidelity page for full sized sealed 'phones
The former two links are lists of open/closed headphones, but they should help you get an idea. Tyll's reviews in the second link are quality.
In terms of individual items, yes the m50s are good and have developed a sort of following as 'starter' audiophile 'phones. Another strong option is the Shure SRH840, which isn't something I've heard but is something that you tend to see being purchased for the price range you put. It apparently has a great reputation for mids/highs for its price range. My personal favorite is the HD25, which is another rock solid contender, but the HD25 (Classic Senns just turning 25 years old I believe) isn't gonna shine up top like reviews for the Shure 'phones suggest they do. The HD25 (this is from my direct experience this time) is gonna throw quite a bit of the treble range at you, but not give it the glimmer of open senn headphones like the 598s. I like the HD25s personally because of how crisp they sound, despite the small soundstage (how 'big' or 'wide' or separated the sonic image they create is). The HD25s have 'punchy' bass in my opinion, that is to say the bass isn't overemphasized, it just has this fun way of being there and making itself known without being too loud.
I would suggest that you don't go with the HD25s unless you get a chance to put them on because they have a way of squeezing your head, and some people just hate the sound.
None of the 3 headphones above have any real visual flash to them, which is good I guess because they can be worn most places without intruding. They don't scream "steal me" like some closed 'phones in this price range.
Like I said, because I was happy with the HD25s for my closed 'phones, I don't have much experience in similar models at this price range. Luckily, this question isn't unique and there are lots of threads like this:
that feature opinions on headphones I have no idea about. There's a lot of "DJ" headphones that fit the description.