<p>As one of those people that never got around to properly learning design (or having no talent for it), the design seems to be the step always holding me back. It's not a problem for rich-clients, as the standard GUI toolkits provide some acceptable ways to design a good-looking interface, but the web is another story. </p>

<p>Question: Does anyone know of a high-quality framework for designing the interface of web applications? I'm thinking of standard snippets of html for an adequate set of controls (the standard html controls plus maybe navigations, lists, forms) and style sheets to give it an acceptable, modern look. If such a thing existed, it could even support themes in the way wordpress, drupal etc. allow it.</p>

<p>I know of the yahoo yui, but that's mostly javascript, though their grid css is a step in the right direction. </p>

I'm not sure that what you're looking for exists in the way you're looking for it. However, I've had some luck with places like
Open Source Web Design
and
Open Designs
, which have some really slick templates that can be adapted to a web application so they at least don't look like crap.
There are also some commercial offerings, such as
Gooey Templates
.
Once you're getting closer to launch, you can contact a pro to fix the details for you, or simply build on what you've got.
Edited to add
: You might also want to consider learning
Blueprint CSS
. I've found it helps guide my layouts and helps them look "right", without constraining me to the layout constructed for another purpose.