F.lux – Better lighting… for your computer
Just giving F.lux a go. It self adjusts your monitors brightness and colour range depending on the time of day and your lighting conditions. After inputting your exact longitude/latitude (the program helps you with that) and what lighting you have you just need to forget about it. As I haven't yet experience it's evening-night adjustments I'll withhold judgement, but I've heard wide praise of this little program. It builds on the success of night-based themes for browsing that are less painful on the eyes, but takes it to the next level.
Oh, it also comes in PC, Mac and Linux flavours!

Keep Flash fullscreen with Ignoflash, great for dual monitor setups
Ignoflash is a brilliant tool which will patch your Adobe Flash dll on windows, allowing you to watch fullscreen flash while working on your other monitor. Usually when you click away from a flash video it loses focus and shrinks back to the original webpage, however with this hack it wont and if you need to shrink it you just need to hit the ESC key.
It supports Google Chrome which uses its own version of flash. 10 seconds to patch and I'm up and running again.
Don't forget, when you're patching dll's it's possible to do damage if you make a mistake, however when using Ignoflash it does actually backup the dll in the same directory so it's easy to restore the original.
Digg Top Ten Normalizer, an excellent Digg Greasemonkey script
Here is a great greasemonkey script called Digg Top Ten Normalizer. It rewrites the digg sidebar to link the stories directly to their respective websites, rather than the comments section - that however is still available below each link.
If you don't have greasemonkey already get it now, it will change how you surf. The Firefox addon describes itself thus:
Allows you to customize the way a webpage displays using small bits of JavaScript.
Along with Userscripts, a repository of GM scripts, it gives any Firefox user the tools they need to make their favourite website that bit more functional.