Yeah I'm a new kid, so I don't know anything, should be ignored, and am making this shit up to sound cool... which isn't going to work because I'm going to recommend the bog standard boring crap...
Lavry DA10 as suggested or Benchmark DAC1. Either would be a nice (not huge, but noticeable) step forward IMO. Hard to go past either for your budget, and if you aren't happy with the 'upgrade', not hard to get your money back via the 'for sale' forums of any site along the lines of www.head-filltheblank.org
My preference between the two is the Benchmark, and I have found the in-built headphone out to be of equal quality to any external headphone amp I've tried so far.
Best of luck with your search...