This is a collection of different commands that I maintain for my own reference. Be advised that most of them will work only on Ubuntu and other Debian derivatives.

Install encrypted DVD support:

sudo wget http://www.medibuntu.org/sources.list.d/`lsb_release -cs`.list --output-document=/etc/apt/sources.list.d/medibuntu.list && sudo apt-get -q update && sudo apt-get --yes -q --allow-unauthenticated install medibuntu-keyring && sudo apt-get -q update
sudo apt-get install libdvdcss2

Stop Update Manager from popping up arbitrarily:

gconftool -s --type bool /apps/update-notifier/auto_launch false

reconfigure X:

sudo dpkg-reconfigure -phigh xserver-xorg

Install jhconnect (JHU VPN):

wget http://panoramix.me.jhu.edu/~jgraham/linux/packages/jhconnect/1.0/jhconnect_1.0-1_i386.deb
sudo dpkg -i jhconnect_1.0-1_i386.deb

Install wicd:

echo 'deb http://apt.wicd.net hardy extras' | sudo tee -a /etc/apt/sources.list
wget -q http://apt.wicd.net/wicd.gpg -O- | sudo apt-key add -
sudo apt-get update
sudo apt-get install wicd

Blacklist rt2x00 modules:

echo -e 'blacklist rt2500usb\nblacklist rt2500pci\nblacklist rt61pci\nblacklist rt2x00pci\nblacklist rt2400pci\nblacklist rt2x00lib\nblacklist rt2x00usb' | sudo tee -a /etc/modprobe.d/blacklist

Compile compat-wireless:

First go to http://linuxwireless.org/download/compat-wireless-2.6 and download the file named "compat-wireless-2.6.tar.bz2." Save it to your desktop. Then run these commands:

sudo apt-get update
sudo apt-get install build-essential
cd ~/Desktop
tar -xjvf compat-wireless-2.6.tar.bz2
cd compat-wireless*
make
sudo make unload
sudo make load
sudo make install

Compile Linux kernel (in eleven easy steps):

#install gcc and ncurses-dev
apt-get install build-essential ncurses-dev

#download kernel source code (any release >=2.4.x.x should work; here we 
use 2.6.30.5)
wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.30.5.tar.bz2

#unpack source
tar -xjvf linux*bz2
cd linux*

#configure kernel (this is optional...if you skip this step you should 
still get a pretty usable desktop kernel)
make menuconfig

#build the kernel (this will take a while, like several hours, or maybe 
days if you have an old computer)
make

#build modules
make modules

#install modules
make modules_install

#install the kernel
make install

#build init ramdisk for new kernel
cd /boot
update-initramfs -o initrd.img-2.6.30.5 2.6.30.5

#add new kernel entry to grub boot menu
update-grub

#reboot!
reboot