My thoughts, having not heard the V-moda, but having recently been trying to decide between them and the DT990:
If you keep your eyes open on Amazon, you can find the 990 pro for around $150-$170. They are great for stationary use, but obviously a no-go for portable listening. In terms of amping, it depends on what you're going to be listening from. I think for the 990 pro, a Fiio e-11 will work.
For another $140, you can score the AKG K167, which are a closed portable and fold up to a really compact size. They have very clear and detailed highs with solid and clear bass. They're not as feature-rich as the M-100, they don't have the awesome visual styling of the V-moda, and the build quality isn't going to be as good. At less than half the cost of the M-100, you can't go wrong IMO. I have had some comfort issues with the cups after long listening sessions, but others have reported similar issues with the M-100. The K167 don't need an amp.
So basically, for the same price as the M-100, you can get two pairs of cans suited for different listening purposes. Others will porbably have more informed opinions, I'm just getting into headphones after years of being content with IEMs.
The other option, if you're really curious about the M-100, is to order both the M-100 and the DT-990 from Amazon, decide between the two, and return whichever one you don't like.