I needed to flash my own bootloaders a few months ago and I quickly realised that its a pain to find what is out there. It seemed like Adaboot never got into a repository and then it was modified and people just had links to tarballs on their web sites.
So I finally found what I thought was the "latest" and was using that. But a few weeks ago I decided to make some modifications. So I threw it into a google code repository for better tracking:http://code.google.com/p/toastedboot/
You can either get the source from there, or you can grab a prebuilt 328 image. I needed to build both 16 and 20 mhz versions for my Lightuino LED Driver board so I threw them up there for all to use.
The major modifications I made are mostly useful for clones that require you to press the reset button to upload:
1. PWM fade the pin 13 LED while waiting for a download. This way you know when you missed the window.
2. Reset double-click. If you double click the reset button it waits for a download for a LOOONG time. This is really convenient when the board is not right next to the computer.
3. A lot of code refactoring for size.
4. All the Adaboot fixes and features of course.