I'm with everyone who has suggested Audio Technica's ATH M50s. I can't say anything about them that hasn't already been said haha, I've had mine for a few years now - they've held up longer than any other pair of headphones i've owned and the quality is amazing. Definitely getting a newer pair of the M50s when these eventually die on me.

I've been using AKG K702s. Semi open back headphones that i got on sale off amazon a couple years ago. Fairly flat response but do need a fair amount of volume. If I have to mix quietly at night i always trust mixing on those.

I think it's worth saving up and going for a really quality pair of open back headphones for mixing. Good headphones are an amazing tool, but you also need to consider a quality headphone amp to drive the headphones especially if they are planar magnetic... it makes a huge difference.

See if you can find and test out Sennheiser HD800's. They are my favorite headphones, the detail is unparalleled. They don't have a visceral bass like some others, but you can clearly hear the fundamental. Also check out the Audeze LCD-X. LCD-X is also really amazing; it's a little more narrow of a sound stage and the highs aren't as bright as the HD800, but the bass is much more visceral  and the detail is incredible as well. I ended up buying both of them over time  If the HD800 and LCD-X are way out of your budget, it's worth trying the Sennheiser HD650's as well.

In terms of headphone amps, Schiit makes really good affordable amps.

Try Audio Technica m50x, i have a pair of them and they're truly the best thing i've ever had + they're made for monitoring so they're flat and have great frequency response.

also have these. tried a friends and bought them immediately. perfect headphones