First and foremost, life is great and it’s Konfabulator’s fault. Thanks to stega for pointers to that. Konfabulator gives you widgets, such as the weather one on the right. I also recommend easyKal, iPod remote, Internet health monitor, iChat bezel, and analogue clock.
Next: SlimBatteryMonitor, via Ted’s Mac tips and tricks.
This one isn’t strictly software per se, but a collection of mighty useful iTunes scripts.
Finally, through clenched teeth: Remote Desktop Connection. Some actually rather good Microsoft software. I’ve used this several times to administer a Windows XP Professional machine remotely, and I have to say: it works. Useful for fixing things on the parents’ computer when it goes wrong.