I'm not sure what the money was that you have available, but with your talent you ought to get something good- I have Sony MDR-7506's. They are highly regarded in recording studio circles. Oh yes, just about 100USD.
My two favorites are the Sennheiser HD-280 Pro (I own a pair) and the Sony MDR-7506 (I've auditioned them). I found the Senns to be more neutral, and the Sonys to sound "prettier". Both are closed, which helps keep the household noises out of your listening environment - especially when the kids are awake.
I like monitoring my stuff on both speakers and headphones. You will hear details in the cans that you won't hear from the boxes, but cans don't image correctly and they won't tell you if a signal is out of phase. Use the boxes for imaging and phase checking. When your material sounds great on both, you know that you've got it right.
The best thing about headphones? For $99 you get a world class pair. They're the best $99 monitors you can buy!
I've heard that the Sony's sound great, but aren't good for mixing becuase the high end is a little exagerrated. Is there any merit to this?
My experience with 7506s is the same; hence, my "prettier" comment. I find the HD-280 Pros to be flatter, but not as "sweet" as the Sonys. I chose the Senns for mixing. The Sonys would be better if you also do casual listening. Both are excellent. I also listened to a closed Audio Technica studio model, but they sounded quite dead to my ears - I think they roll off the highs and lows a bit.
Hopefully you can find a place to audition the Sonys and Senns (and maybe the ATs). It's best to make the final selection with your own ears. And then please buy them from the place that gave the demo. They may charge an extra fiver or so, but they would have earned it, and you then don't need to wait for delivery.
I use Grado 225 cans with a tube headphone amp I built from a kit (Mapletree Audio Design Ear+) Very happy with this rig. A lot of fun to listen with. You might want to check out the HeadFi Forum. There's a bunch of nuts there who live and breath headphones.
I like the Grados as well. The biggest complaint with them is that they are uncomfortable to wear for long periods of time. Of the ones I tried, I felt that way also (although I did not wear them for hours on end - they just felt like they'd be uncomfortable).
I am also partial to Sennheisers (the HD-590 and HD-600 are excellent but pricey in comparison as well). I own a set of HD-280 and, for the price are great IMHO. I feel that in order to mix properly, you need to use speakers of some sort. I find it difficult to accurately judge such things as panning, reverb, and delay when using headphones.
Using a combination of listening through phones and speakers yields the best results for me when mixing.