So I had a quick look around for a nice application to use for forms design. There are a few specific tools for it but most are quite expensive or very early alpha or beta apps. I wanted something free as I'm not working on a major app now. In the end I decided on trying out Inkscape for now.
One thing that I found that made me decide to try this was this page: http://mairin.wordpress.com/2010/08/02/creating-ui-mockups-in-inkscape-v... . I've just finished watching the video (I found it on youtube as well http://www.youtube.com/watch?v=1yH6IMydxdQ&feature=related ). I've not followed it totally as it's quite easy just to jump into Inkscape since I've used tools like it before.
So back to the design. I basically created the same as the last time but I've moved the buttons around a little bit. I think it's a lot easier to use this then on paper. I figured that I could create a template of different UI elements in a separate file. Then I could copy and paste them into new designs, or even duplicate a whole design to start a different idea or format.
Since the ListConverter is going to be quite a small app I might not do any more design but just go straight into the form designer soon. Also since I am designing the app mostly for my own use I can't ask myself or an opinion in the same way as I would if I was designing it for someone else :).
Also another good looking site about Inkscape: http://screencasters.heathenx.org/ . Near the end of the last part of the youtube videos (part 5) a guy suggested the site.