We'd heard for several years at the Shareware conferences about doing bundling and things to try and sell more. But we never had the products to do it.
After the conference in 2006, I just decided to make some so we could do it! I made a couple little tools (actually extracted parts from a bigger program). Some things that were very obvious and easy to understand. Especially the "Where'd My Space Go?" is easy to understand with the name, a little text, and a picture. I eventually added a friend's screen-saver as another choice. I wanted several very different things--something for everybody.
We did simple checkboxes on the buy page to add them to the orders. And really cheap prices. Make them like the goodies at the checkout in a grocery store--a real impulse thing to add the $5.99 extra tools.
It has worked well. Most days about 10% of the orders add one of the items.
We've also done the tools as standalone programs--with really no promotion. But they've gotten a few sales that way too. The tools we did are available through RegNow's affiliate program, so if you want to try with ours before making your own, you can do that too.