You can stream this year's Mac World keynote address from here.
The iWork Suite, Apple's answer (replacement) for MS Office. Alternatively, you can check out NeoOffice/J 1.1, which is a free Office-like suite with some pretty hefty minimum requirements; can't beat the price, though.
You can find optimized versions of Firefox for G4 and G5 processors here. It works noticeably faster on my G4 Powerbook.
SlipStream software will untether your AirPort Express from being forced to use iTunes. I like iTunes and use iTunes, so I don't really care, but if you have a big Real Audio or MS Media Player collections, this should be pretty cool for you.
Mac Software Update tips from this post on Daring Fireball.