When faced with the same situation (3 years ago), I decided to train myself to at least be able to create decent looking UI.

It's not that hard, if you read a few books and practice a bit, to be able to cover 80% of design needs (and you can stay in the code these days, ie: work in CSS3 and take screenshots for instance - staying away from Photoshop).

You can also subcontract to a UI designer for the inspirational bits and do the rest of the work yourself.