As in title: What to get for my SRH440 around 80 - 100 USD? Since the phones aren't exactly bass heavy, I guess I should buy something warmer, like SONYs perhaps? I had a Fuze before - don't know, but I had a feeling it sounded a tiny bit underpowered or something.
You should never buy a source for a specific pair of headphones. It should normally work the other way around, but since you already have the headphones I guess it is different. Any DAP will be fine. You could give the Fuze (or Clip+) another try and Rockboxing it (I'm using the EQ on my iPod Classic and I LOVE it!). I personally recommend Cowon DAPs. The JetEffect settings are great. Check out the new Cowon C2.
I have no experience with Sony DAPs.
EDIT: I didn't pay attention to the fact you called the Fuze under-powered. I'm not sure, since I've never had one. I can personally state that my Cowon S9 has no problem driving full sized cans at all.
if you have no plans on getting an amp or anything extra like that then get a cowon j3. The 8GB model may be a little out of your price range but it's really the best dap if you arent going to use an amp or anything. You can add sd cards for more storage or you can spend more and get the 32GB version.