I think what we need is a new hardware category... or a drastic design change to hardware... the Athlon-64 fits into that category... but when it's released, will there be a 64 bit version of Windows?
We need some new technology that's not extremely expensive. Maybe if one of the video card manufactuerers made something like, a dedicated AA and AF processing unit... kinda like a GPU with 2 cores.
Serial ATA isn't anything to get excited about... the Raptor on the other hand is quite nice. Most of the complaints people have about a computer being slow can be remedied with a fast hard drive... but the Raptor still can't keep up with the demands of a 3 Ghz processor and programs that are 2-3 GB in size. Affordable solid state hard drives would definately be an interesting thing.
I think Windows needs some changes made too... Longhorn sounds like a big change, but I don't think it's a significant enough change to increase hardware requirements. I've always though a 3D Windows GUI would be great. That would require a good 3D video card, maybe a new mouse design, more and faster RAM. And a faster hard drive wouldn't hurt either.
I also think Microsoft would do themselves a huge favor if they built another xBox with more PC-like capabilities... maybe make an xBox 2 that's got Windows XP's Media Center Edition that allows you to browse the web, play games online, and run a home entertainment center from it... hell, they could even make xBox 2 that can play regular PC Games.
And those aren't the only things that are lacking... the internet is becoming very boring. I think it would be a good idea for bands and singers to make their music available to download online for a reduced price than if you went to the store and bought it. And software companies as well. I think with broadband, the internet can be more interactive than it is... sell software that's on the internet... in other words... you pay for access to a program on a website... it's never actually installed on your computer.