I've used both balsamiq and Irise with great results @ client sites. My first iRise experience went great. The client developed two pages of specs for an ERP integration project over a months time. Within two days of using a proto-type we threw away those specs and were able to show them what they had really wanted. When you are dealing with UX issues and people who don't code it's so critical to show the client upfront what is going to happen. I can't tell you how many hours of rework we saved by having discussions of workflow, textbox locations and other seemingly minor ux elements. Once we are done with the mockup and the flows are defined it's very hard for someone to screw up the code. Overall great experience. I may write a blog detailing some of the finer points one day.
I did this in my last consultant project, and it turned out well but with some difficulties.
Before, I photoshoped the webpage (main page, and maybe some thing else) and then meet with the client to make the modifications, so that ,with the design done and closed, I could keep coding to finish the page. This turned out by the client in like huge focus on the design asking for lots of changes because they couldnt really imagine how it was going to be in the end.
Ultimately, doing it on reverse turned out to be more revealing and useful.
Fist map the pages of the site. Then html prototype all of them with simple styles.
The hard part is explaining the client that this styles have nothing to do with the final design of the site, and that its all about structure of it.
After the changes, the website is pretty much done in terms of big changes, so it gives you room to code knowing that bit less of the structure will change. Then at the end, I do design and iterate with the client until their happiness.
