The OP hasn't named a price point yet, but if he's willing to spend a few of the suggestions above would make sense.
The KEF M500 and Mad Dog are some of the most oft-suggested options if by "balanced sound" you truly meant something relatively neutral across all spectrums, but both of them violate one of your main requirements. The M500 sits on-ear, and the Mad Dog can get unbearably hot after awhile due to its massive Alpha Pads. In addition, the Mad Dog with Alpha Pads has some clamping issues for some people, though my head is small enough not to have those problems. The MD also really should be put in a setup with a headphone amplifier to shine, so if you want a casual can to plug into an iPod or computer they won't be for you.
If you like some bass boost, the MDR-1R and D600 would probably be decent choices (though I haven't personally owned the D600 and can't confirm what others have said about them), but both of them suffer from the same cushy leather pad issue that the Mad Dog does. They're comfortable at first because they're extremely cushioned, but get hot and stuffy after an hour or so.
I think what you really need is a relatively lightweight can with velour earpads, something like an HD5xx, but closed. Perhaps a Fischer Audio FA-003/Brainwavz HM5/LINDY Premium Hi-Fi (they're all the same headphone marketed under different brand names) would work, but I can't recall which versions come with velours and which come with leather earpads so somebody else would have to chime in. At the time that I purchased my pair the FA-003 came with one leather pair and one velour pair, but that could've changed over the last two years. In addition, you will probably have to stretch them out considerably for them to be comfortable long-term, since they were even tight on me when new.
The Koss Pro DJ100 are super-lightweight and have a mid-centric sound with plenty of treble sparkle, but their cups are too small to be truly over-ear unless your ears are tiny. If you hadn't specifically stipulated a fully over-ear design, they'd be at the top of my recommendation list. Something similar to them with larger earpads and higher build quality is the Pioneer HDJ2000, but those might be a little on the bassy side for your tastes.
There's a lot of variables here, so I'll refrain from naming any more suggestions until we have a price point to work with and a clarification on whether over-ears are completely out-of-limits or just discouraged.
