The M-100 and MDR-1R didn't seem too impressive based on measurements I've seen, and I've heard mixed subjective impressions on them as well (Note: I tend not to frequent HF impression threads, as you're almost guaranteed to get many people loving on anything no matter how bad it might actually be). I'd do a lot of research on those before purchasing, though you might decide that's what you're looking for.
If you're interested in the HD650, you really need to consider the Mad Dog. From what I've gathered, they're both fairly neutral but tilted towards a darker/warmer side. You can't go wrong with either (or the HD600), but you would need to decide if an open headphone would suit you OK. I have read reports of people needing to swap out the pads on the HD650 every couple years depending on use.
The nice thing about the Mad Dog is that you'll save money compared to many other comparable sets. I'd use that extra $200 towards something like the Schiit Modi/Magni combo, because the MD really benefits from a strong DAC and amp. Or maybe you need a portable amp. Or maybe you just want to pocket that extra $200 you'd save compared to your $500 budget. ;)
Edit: I just saw that you mentioned wanting a HP that would work OK without an amp. I can't speak for the HD650, but the Mad Dog works rather well off portable sources. I tried it out of an iPhone 5, and it sounded good. It lost some of the heft and bass, but it still had some punch to it (it wasn't bass light). It didn't get crazy loud, but it's enough for most music (it helps that the MD is closed-back). It sounded even better from my HTC One (volume was about the same, but some of the missing bass came back). Based on impressions I've read, the HD650 doesn't do as well from portable sources. I have never used a HD650, so I can't verify.
I also saw you mentioned wanting a D2000. Having had one, you could expect somewhat big bass that is a bit muddy (not bad, though), recessed mids, and treble that can be a bit bright, rough, and sibilant at times. The Mad Dog, in comparison, offers what I'd consider to be better/more neutral bass (still plenty of it), better/more pronounced mids, and a smoother top end that doesn't have any less detail than the D2000. It's a cleaner, smoother, more natural sounding headphone overall, IMO.
I can't stress how great of a value the Mad Dog is in its current state. Plus, Dan (MrSpeakers) has a great 15-day return policy if you decide they're not for you.
Edited by hans030390 - 8/4/13 at 12:23am