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 in

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.