This is an index of threads on how to get the best performance out of your Ubuntu machine.
Warning: These tutorials may cause harm to your system if you do not follow them correctly. Please remember to carefully follow and read the guides. Thank you.
Use InitNG as a replacement for standard Init.
Speed up Firefox
Custom compile a new kernel. You can also use this tutorial.
Make sure DMA is enabled.
Use Prelink to make applications start faster.
Pick the kernel that's right for your processor.
Disable uneeded services from starting.
Use Swiftfox, a faster Firefox for Intel and AMD processors.
Tweak your ext3/reisers filesystem for enhanced performance.
Clean up unnecessary files
XML Optimization Thanks to orvils for the link and informmation.
Tips from me:
Install preload "sudo apt-get install preload."
Use the latest drivers for your video card.
Use XFCE as your Desktop Enviroment.
Use Abiword instead of Open Office