If you just need to change things up, try a Fiio E6 portable headphone amplifier for about $30 US. It has 4 EQ settings and can change things up.
HD 600's on a laptop is not really a good idea without a headphone amp, as a matter of fact there are not too many quality open backed headphones that will sound great unamped.
If you like the E6 you can move up to maybe the Fiio E12 ($120US) or JDS Labs O2($175) or C5 ($175). Get the O2 if you don't plan on moving around much or the C5/E12 if you travel a lot.
If you just want different headphones and no headphone amp, Try the V-Moda M80, it's sweeter midrange than the new M100, a better for an unamped laptop BUT the 600's have better separation than soundstage. The M100 has much more bass and is louder than the M80.
I also recommend the Marshall Monitor headphones, very flat and neutral with the highs a bit recessed for smoothness/warmth, but near or at the top for separation on closed headphones. They are also capable of being driven fine without a headphone amp. The problem with the Marshall is an estimated 100 hours burn in before they sound great. V-Moda pretty much sound great immediately.
If you get a headphone amp and STILL want another set of decent headphones, I recommend the Ultrasone HiFi 2400. Better separation and soundstage than the 600's, as a matter of fact to my ears they're extremely close to the HD 800 in terms of imagery, but the 800's have more clarity on the bass. The 2400 sounds a lot more expensive than it is and is definitely in the same room with a lot of high end headphones, including high end Ultrasones.