UI Prototyping Tools

I have been a fan of paper prototyping for many years. Paper prototypes are easy to create,  easy to edit,  and easy to scan and distribute the same as if it was created with some software UI designer. They also put your mind in a different mode - writing with a pen or pencil and paper is a lot different than sitting in front of the computer using a mouse.

There's just one issue - my office doesn't have a scanner. Now, that shouldn't be too hard to remedy, but along with my list of benefits to paper prototyping, there are also a couple of drawbacks.

• When there are many states to a given UI screen, it can result in a lot of repetitive drawing
• It can take a long time to sketch detailed layouts of more complicated UI components

This has made me once again curious about UI prototyping tools. I probably last looked at the available options 4 years ago.

To start things off, a coworker discovered Balsamiq Mockups. This looks like a pretty fast and easy to use mockup tool. It's quite possible I could create mockups faster in Balamiq than by hand, and they have a sort of notebook-sketch quality to them - they don't try to look like a real UI, and I like that. It also has JIRA integration (as well as some other issue tracking systems like FogBugz and some wikis), which could be a big win for us if we adopt it.

I'm curious what else is out there. I've read a couple of questions about this on StackOverflow to get some ideas, and WireframeSketcher also looks promising (it's an Eclipse plugin).