The About Gardening Guide has a great list of free plant and seed catalogs than you can order. At this writing, she has links to the free catalogs listed below. With all of her listings, Deb lets you know whether they can be ordered worldwide, just from the US, US and Canada, etc. If you click on any of the catalog names below it will take you to the Gardening Guide's free plant and seed catalog page where you will find the actual links to order the catalogs.
Don't forget to visit the About Gardening Home Page for much more great gardening information.