Anything you're planning on growing has an "heirloom seed." These are open-pollinated (non-hybrid) seeds. Hybrids are what you'll find in most seed catalogs, since they are bred to produce disease resistant and pretty plants. When you try to grow a seed that came off a hybrid plant, only some of the characteristics bred into that plant will result. For instance, say you decided to save the seeds from your BigAss Tomato that you got from Burpee. It will probably produce a tomato plant, but it may not be so big, or it may be real big but not so tasty, or it may be big & tasty but not disease resistant.
Here's where I buy all my seeds: www.rareseeds.com. I don't know why that's their URL but their company is Baker Creek Heirloom Seeds. I'm sure there are other companies around too.
Next week'll be February and I'll be starting the eggplants, tomatoes, peppers, petunias (yeah I'm gonna try 'em again this year), and echinacea. Most of which are from seeds I've saved from previous years. Yes, this means I DIDN'T HAVE TO BUY THOSE SEEDS THIS YEAR!!!!