In order to pick the right amp you must first have as much understanding as you can about the dr150's. I have em too just to clarify.
The thing about it is that has a very "in your face" sound stage. Depending on the songs you listen to, some of them can even end up feeling like the vocalist is singing in the back of your head from the inside... To some, this can be a bad thing. But personally I find that live recordings sound really good with these cans. You won't get that invasive feeling through one of those.
Then you should know that the high's are quite well defined and sometimes can be a bit strong (due to the sound stage). Mids are not very strong but you can hear it. Lows are nicely defined and personally I find this the reason why I love these cans.
So... when you choose an amp, you should probably avoid amps that sound too bright (with that in your face sound stage, it's going to cause headaches). You don't want an amp that over-emphasizes the bass either otherwise everything will sound muddy.
You should probably get a nicely balanced amp with a nice large soundstage... or another way to put it, one that sounds like the band is really playing in front of you and you're right in the middle of the audience. Sorry for the metaphors but choosing the right synergy for your headphones is an art, which means it's totally subjective. Since the dr150's have a compressed feeling soundstage, an amp that spreads the soundstage effectively will sound good.
You should also look out for amps that really bring out the mids since that's another weak point about the dr150's.
Oh and another thing you should know is that these cans operate at 32 impedance... This means that an amp with too much power will probably be pointless. The lesser impedance loosely means that your headphones don't need much power to get them pretty damn loud.
Because of the low impedance, you shouldn't spend too much on your amp either. If you're going to blow cash on a really powerful amp then you're only going to end up replacing your dr150's.
Hope this helps. Personally I use these headphones without an amp and use it straight from the source.
Just FYI, I'm currently using an ibasso D1 which has a rather bright amp. Basically it's actually a "top class" DAC with an integrated amp which some argue goes well with the DAC. Because of the bright sounding amp it can kinda get a bit harsh with the dr150. Since I've already made my purchase I've decided to try something out interesting...
I actually had an old Rotel loudspeaker amp which I used for a while that had an integrated Headphone amp which went well with the dr150's. It warmed up the sound dramatically and made the soundstage sound more open. Definition wasn't it's best feature but that was because I didn't have the ibasso D1 for a DAC and I used my X-fi soundcard line out as the source. Right now, the Rotel is under repair because of grounding issues.
When I get the Rotel back I'm going to bypass the ibasso's amp and use it's line out which will go into the Rotel. Can't wait to try that out. It may be the balance I need. Based on what I've been hearing the ibasso D1 is more of an excellent DAC than it is an amp.
I would love to hear what you will be doing and what you discover along the way.
Also, about the dr150's, most headphiles that have tried it say that it's soundstage is very similiar to the Grado soundstage. Some have criticized this as a "flat 2d soundstage" but mind you that depending on the music and individual this can be a damn good thing. This little info may be helpful when talking to whoever you're buying your amp from. That way they will be able to gauge something suitable for you. Personally, I'd recommend you bring the dr150's out with you to test them with the amps before you choose one if you can. If you can't test em, then I guess that Grado analogy may prove useful.