Ok, just going to throw out some accessory ideas here, with alternatives if I can. I love spending other peoples money
Headphones:
Sennheiser HD515 Stereo Headphones (SP-018-SN)
-or-
Sennheiser HD555 Stereo Headphones (SP-019-SN) [[My pick]]
-or-
Sennheiser PC160 Pro-Gaming Headphones (SP-014-SN)
I don't use a mike, hence the 555 as "my pick". Decent all-rounders for gaming, audio and movies. The 160's are good so I'm told. I've never used them though. Sennies rock the casbah, regardless, and represent a good deal for the money.
Keyboard:
Saitek PZ30AU Eclipse Illuminated Keyboard - Blue (KB-015-SK) [[My Pick]]
-or-
Logitech G15 Gaming-Grade Illuminated Keyboard - Retail (UK Layout) (KB-077-LG)
I don't really like the G15, but it's a visual thing. It's too bulky for my tastes, but a lot of people love em.
Mouse:
Logitech G5 Gaming-Grade Laser Mouse (KB-069-LG) [[My Pick]]
-or-
Razer Copperhead Tempest Blue 2000dpi High Precision Gaming Mouse - Retail (KB-015-RA)
I just like the feel of the Logitech. The Copperhead's an awesome gaming mouse though, and comes in more colours than the one I listed. Blingy!
Speakers... I have some pro-audio monitors on my desk, as that's my thing. Not sure what's the best pick there, I'm sure someone can post their advice.
One thing is for sure though. You've got a sweet sound card there, you definately want some good quality speakers or headphones. If you have them already, cool. If you haven't, that should be the first upgrade for you.