Bountiful Gardens is one of those catalogs that make you feel all sustainable and tree-huggy just browsing through it. They are a California-based project of Ecology Action, promoters of the Biointensive method (John Jeavons, double digging, intensive planting, etc.). The seed is mostly West Coast-grown and the descriptions don't necessarily take our Mid-Atlantic climate into consideration, but it's worth a look. For vegetables, selection is pretty good (open-pollinated varieties, many heirlooms) and prices are quite low. This may be the place to find seed for that unusual plant you wanted to grow; it's where I first found seed for sea kale and for Egyptian spinach or molokheya.
I'm also very keen on their seed mixes and seed collections - the mixes are just fun if you want, for example, to try multiple varieties of turnips without buying a pack of each, and the collections would make good gifts for a beginning gardener. They have good selections of slow-bolting lettuces (for California, at least; I'll see how they do here) including both a mix and a Summer Salad Collection.
I refuse to double dig, though; it hurts my back.
Notes: (1) You can order a print catalog through most of the catalog
websites (or in some cases, download a PDF version). (2) Mention of specific products, brands, or companies is not
intended as an endorsement by the University of Maryland. (3) I do not
receive consideration of any kind for mentioning products, brands, or
companies in my postings. The seed catalogs I review are those of
sellers from which I have previously bought seeds.