Common Web UI Styles

A combination of 960gs for layout and jQuery-UI for styling is probably what you are after.

You could also consider the blueprint CSS framework instead of 960gs.

What about using dojo and dijit?

Dijit is a fast way to create widgets and elements. It also comes with 3 default themes which are easy to modify.

A good list of different widgets here

I can't believe nobody has mentioned:

http://www.extjs.com/

Its a commercial js frameworks, but pretty affordable, and makes putting together a nice UI a breeze. There's a much more complete set of elements then jqueryui, and its designed to make an entire app. I've only played with it a little, but I really love it so far. Free for personal use.

If you really want to get a feel for a complete UI developed with EXT, try this url:

http://docs.sencha.com/extjs/4.2.1/extjs-build/examples/feed-viewer/feed-viewer.html

Pair up with someone who specializes in UI design.

If you are better at dealing with business logic, your time is better off spent exclusively coding business logic so you can master it. This will require you to learn how to interface with someone else who excels at presentation. (xml and json are common means)

Business logic and presentation are very different. Designing a system that not only looks good, but is intuitive and easy to use is quite difficult. Equally as difficult and time-consuming as establishing the inner workings of a complex application.

A good interface is not as simple as including a css framework.

I consider myself to be a more 'creative' programmer who does excel in presentation. I happened to be lucky enough to cross path's with someone who was, first of all... very motivated, and second of all very good at 'business logic'. He had a lot more experience planning and implementing complex systems, while I mainly have been focusing on interface design.

If you are more productive doing system architecture, planning, developing, whatever... you should push yourself in that direction. While solo development projects can be rather fulfilling, I view it as inefficient. It is very rare that someone possess skills to develop top-level applications solo.

The challenge is finding someone who you work well with.