If you haven't upgraded to Windows 7 or are looking for a new version of Office, don't head to your nearest retail store/website just yet. You may have a cheaper option. If you are a student or teacher chances are that you qualify for academic pricing. Microsoft's web page with more information can be found here. You may have better luck, however, asking someone at the campus bookstore or checking your school's website for specific deals.
Another option I just read about on CNET's Cheapskate blog is Microsoft's TechNet subscription service. Basically for $200 you can download almost any piece of Microsoft Software for up to 10 computers (non commercial use). This includes Windows 7 and Office. A full list of available software can be found here (xlsx file). For more details on this product/program I recommend checking out the blog post on bnet.
USB drives (thumb drives, usb keys, jump drives, whatever you call them) have dropped in price dramatically. I think I paid around $80 for a 1GB drive 5 years ago and now you can get a 2GB or even 4GB drive for under $10. With these drives so cheap (even given out by companies at trade shows) are you taking advantage of all that can be done with this portable storage medium? Below I've listed a few things that you can do with your drive besides carry your documents and spreadsheets around.
Portable Apps
http://portableapps.com
http://www.pendriveapps.com/
Portable apps are great for people who use multiple computers and have specific programs they want with them at all times. They are also great for anyone who does any troubleshooting/it work. The programs reside and run completely on the usb drive requiring no installation on the host computer. See the website for more info. This concept works with OS X, but is much more common with Windows programs.
Manage Passwords
http://cnettv.cnet.com/make-most-your-usb-drive-manage-passwords-your/9742-1_53-19556.html
This video is a couple years old, so there may be more up to date programs, but the concept remains the same.
Back up critical files
http://cnettv.cnet.com/make-most-your-usb-drive-back-up-your/9742-1_53-19558.html
Same applies to this video.
Add extra memory to your PC
http://cnettv.cnet.com/use-flash-drive-memory-windows-xp/9742-1_53-50004761.html
This could be a way for you to use one of those extra drives you have lying around to get a little more performance out of that XP machine.
These are probably just a few of the things that can be done with these readily available, cheap drives. As always, if you have more suggestions, please let me know.