One way to do this is to download the .deb packages from a web browser. From there you can put them on your usb and move them over. Once they're on your Ubuntu box, you can install them through the Software Center (by clicking on the icons) or from the command line with
dpkg -i appname.deb .
An easy way to grab the .deb files is to visit http://packages.ubuntu.com/ From there you can select your version (or just go straight to one such as http://packages.ubuntu.com/maverick/ ).
It can be a little tricky to see what to click to download, but once you've found something that sounds interesting, you'll go to its page, and look for the "download whateverprogam" section. There will be a box that lists the packages -- most have a hyperlink that reads "all" . Clicking that will take you to a download page.
As pointed out, dependency management can be painful using only this solution. Keyrx does sound like a better way to go. One of their pages makes its utility more obvious to me (keyrx):
- Runs on Windows, Linux, and Mac OSX without installation
- Works from a flash device for simple and quick management
- Provides a full independent package management interface (does not
require an Ubuntu installation on the
machine you are using it on)
- Easily download packages and their dependencies
FullCircle Magazine also has a piece on "Offline Package Install" on page 14 of issue#32 (Aug. 2009) (the English language pdf is here but it is also available in other languages here : fullcirclemagazine.org/issue-32 ).
In addition to keyrx, it also mentions AptonCD (which sounds more appropriate for backup of packages or package collections), and generating a script from Synaptic (which is a feature built in to Synaptic).