Headphone amps HD what are the choices?

I'm lost a little..pretty new to headphones :p

the headphones out of the sound card i will be getting the is not really good compare to the quality of it's normal line out..the stereo dac that was used + the small amp doesn't give any good headphone justice in quality ( the signal range is pretty bad also)

i will be purchasing HD-580 or Hd-600 in maximum 2weeks

so i'm on the market for a small good quality headphone amp
i need something that will match up good with the sennheiser's and something that will leave the sound untouched as much as possible
i am on a really tight budget
and i don't know anything about headphone amps!

SO this is where YOU knowledge people come into play! I need advice on what to look for, what kind of $$$ will i be paying for what range of quality ( i do not care to buy used at all)!!

Did i say i was on a tiite budget? hihi :)

Thanks all for your time and comments :)