Denim (<a href="http://dub.washington.edu/denim/)">http://dub.washington.edu/denim/)</a> is kind of interesting. It's a Java Application with an "interesting" UI (seems a bit ironic). It's probably worth a few minutes of downloading and checking out to see if it suits your style.<p>Personally (and I'm more of developer than a designer), I'm with wammin, pencil paper or many white board sessions are where I start for the first few dozen iterations. The last thing I want is yet another tool to get in my way, providing more complexity than value. Once things settle down, or if you have to work with off-site people, electronic versions make a lot of sense.
I use InkScape for wireframes. It saves everything as SVG so the files are easy to send to people I'm collaborating with, and they can open in Illustrator if that's what they're using.<p><a href="http://inkscape.org">http://inkscape.org</a>
OmniGraffle <a href="http://www.omnigroup.com/applications/omnigraffle/">http://www.omnigroup.com/applications/omnigraffle/</a> + free web templates from here: <a href="http://graffletopia.com/">http://graffletopia.com/</a> <p>It's an excellent way to get stuff done. OG and templates have saved us a ton of production time and wireframes that we creted were very clean and most importantly, they were clear and anyone who looked at them would know how stuff worked and how things were connected. OG allows you to add the right amount of detail without wasting a ton of time on minutia that creeps up if you use PS.
Before I design a web interface, I usually like to sketch it out to organize my ideas. I'm still using good-old graph paper and a mechanical pencil, then will often scan my sketches to post on our internal wiki. Are there better tools out there that would maybe allow for sharing & collaboration?