Looking for suggestions on an upgrade

Not quite sure where this belongs but here goes:

I decided that i'd like to upgrade my current PC setup and i was wondering what you might suggest upgrading.

My PC specs:
CASE: NZXT Tempest

CPU: quad core q6600

MOBO: Asus p5q pro

HDD: 2 Seagate 250gb, 1 WD 500gb

DVD: 2 read/write not blueray

2 Monitors (22'', 19'')

GPU: 4870 1gb version

RAM: OCZ Reaper 4gb

PSU: PC Power & Cooling 750W[/url]

I've got good headphones, my speakers are not very good. They are low quality, but i'm in a place in which i cant use them very often.

My keyboard and mouse are the common wireless keyboard

Any suggestions on what to upgrade, or a new part/accessory to buy?

well my budget could change depending on the part but around $200 - $250

I use it to listen to a ton of music and watch movies, playing games like crysis, internet browsing and programming in C++ and other languages. Pretty much everything