I found this on the debain forums, and thought it might be useful to repost here. With these commands, you can list all the packages that are installed on one debian/ubuntu box, and install them elsewhere really easily. This is useful when migrating services from one box to another, the lazy way.
To get a list, and dump it into a file:
dpkg --get-selections > installed-software
scp that file to your target machine:
scp installed-software root@host-I-want-to-move-to:/root/installed-software
on the target host run:
dpkg --set-selections < installed-software
sudo apt-get install dselect
sudo dselect
In the dselect menu, just hit install and go get some lunch. It may take a while to download and install everything.