Ive done alot of work with aspiring DJs lately, and they all seem to have this problem. I tend to steer them towards Macbook Pros and a 3 year warranty, as it seems this problem is pretty common. It has come to the point where I loathe these guys because they always seem to come in on a Friday afternoon, needing their computer in a few hours and having all week to come in. They get pushy and fairly rude because their ass is on the line, so these tend to be the guys I cut off and refuse to help in the future.
That being said I generally recommend the ExpressCard units because it is far cheaper and less of a headache to replace if they wear them out. I found one here:
http://www.amazon.com/Creative-ExpressCard-Blaster-Xtreme-Notebook-70SB071000000/dp/B000QRV3NU
That is a pretty high end one, though I know I have purchased some for around $50 for a less feature rich unit. I dont like the USB ones because the audio quality is very poor, and I am not an audiophile. However, I have used this product:
http://www.newegg.com/Product/Product.aspx?Item=N82E16829102036 in a pinch and seems better than most others out there.
Good Luck.