Improving Laptop Audio Quality with Headphones

I'm looking to improve the SQ on my laptop and I have relatively little idea as to where I should start. I don't want to drastically compromise portability and cost is a factor. I don't need the best quality out there, just something passing, I want my laptop to match my cell at last.

Hello, I have the following

Toshiba Satelite T135-s1305wh, uses Conexant Pebble High Definition Audio
Samsung Galaxy S Captivate w/ Voodoo Sound mod, uses Wolfson's WM8994 DAC
Custom PC with realtek 882ALC + entry level onkyo reciever(not sure of model)

BeyerDynamic DT 770 Pro (80ohm)
Sennheiser HD 280 Pros (64ohm)


to assign subjective numbers -
Music on my gaming PC sounds great to me, I'd give it a 9/10(8/10 on HD280s), it's crisp and clear and powerful. Everything works well or at least well enough. Someday I'll get a soundcard, in the mean time I'm a starving college student.
Music on my cellphone is acceptable I'd say it's a 7.5/10 (6.5/10 on HD280s) which I passing for my day to day. My laptop is a 5.5/10(5/10 on HD280s) with respect to sound quality.

I want a relatively inexpensive solution that will boost my laptop's SQ to something in the same level as my cell phone or higher. If it can improve cell quality that's a plus. What should I be looking at? Portable Amps? DACs? I'm relatively ignorant of such matters and don't know what I need, just what I want. I'm not looking for perfection. What I get needs to be small enough to fit in an already nearly full backpack with a laptop, 1 or 2 hardcover books, a calculator and a couple binders.