As an alternative to Photoshop and Markup you should also try my app, jMockups [1], a web based high fidelity mockup tool. I launched it on HackerNews about a month ago [2] and you can already mockup most existing sites with it. You could create the mockup in this tutorial in about 10 minutes (complete with the gradients and 960gs integration). If I wasn't on vacation and using my iPhone at the moment, I'd show you :)
Just checked out jMockups, great stuff! About the implementation, I see everything seems to be in "canvas", why not just use DOM and HTML elements directly?
Long term I'm going to implement a feature that let's you toggle between low fidelity (sketched) and high fidelity. That would be next to impossible using standard HTML elements. It winds up being a lot harder to implement this way but you get a lot more flexibility too.
Great to see another innovative web-based prototyping tool, Matt! I tweeted about you and added your tool to the @quplo/prototyping list on twitter.
I'd love to write about jMockups in our blog, but I try to keep our posts limited to truly interesting apps. Could you summarise a few really unique features that only jMockups has, compared to competing wireframing and prototyping tools?
I really do need to get some examples up there...
[1] http://www.jmockups.com
[2] http://news.ycombinator.com/item?id=1829657