I usually avoid headsets, but Sennheiser PC 320 accidentally found a way to my place a while ago. Surprisingly good (except build quality though) and quite common around €20 refurbished, at least where I live. I mean, really. Great comfort, unless you have huge ears; pretty nice sound stage; overall quite good sound (don't believe bassheads that it lacks bass).
Otherwise, I'd look into some superlux/takstar/whatever, separate mic and some decent budget-level source.
BTW the xonar U3 is crap, if you ask me. The official drivers are horrible and even without them, it's all over the place (cracking on some setups, great sound on others).