I wonder how many people still use Photoshop to create mocksups first and then move to HTML/CSS. Ever since CSS3 became popular I create my mockups directly in HTML/CSS3.
I prefer Illustrator, it's more "element-oriented" if you will. Easier to move things around. Even if it's lacking a good UI for styling.
If you're missing the UI for styling, you might try Fireworks.
The idea that Photoshop should be used as a layout tool is an unfortunate accident of history -- it was/is the household name for image manipulation as most designers and developers hit the web. But while it's good for raster/photo editing, sets of pixel layers doth not a good layout/design tool make.
Illustrator's a lot better for this. And Fireworks is made for web layout and screen graphics, has a great mix of vector and raster tools, and is evolving some really sophisticated export abilities including some of the CSS export facilities CSS Hat is doing.