Years back, before they moved out of Yankton, my dad was a Gurney's guy and that stuck with me. But, now, the one I buy from is called Jung Seed Company (www.jungseed.com). I don't buy much from catalogs but I like Jung because they offer a different selection than most and I usually try a thing or two out of the ordinary every year. They also don't charge as much for shipping and handling (only $4.95 if you order seeds).
This year I'm going to try Autumn Star Kalettes (a cross between kale and Brussels sprouts). Also, an Everleaf Emerald Towers Basil, which is a more columnar plant, and some Super Heavyweight Hybrid Peppers that I will start in my hothouse. Supposed to be monsters. We'll see. My luck with starting peppers is spotty.
On the tomato side of things, I plant certified organic seeds around St. Patrick's Day and move them into the garden around Memorial Day weekend. I order those seeds from Gary Ibsen at tomatofest.com. During their sale in January, I get a buck off a pack. The packs go for $3-$4 each. And the seeds still have great germination rates 2-3 years later.
I usually don't mess much with planting peppers by seed (run out of room in the house and they seem awfully tempermental), so I buy plants locally at Nachtigal Greenhouse and/or Jolly Lane Greenhouse. That's also where I'll usually pick up few cucumber plants as well.
On the flower side of things, I generally plant seeds for native pollinators (coneflowers, daisies, Black Eyed Susan, etc.) and have good luck with an online place called cheapseeds.com. They're cheap, as the name suggests, and they send you a million seeds.
As for trees, which I'm about running out of room to plant (oh, just kidding, I can always find room) I'm also a cheapskate. I've purchased bare root trees from a cool nursery in Belle Fourche and I buy trees in the late spring/early summer when the stores start selling them 30-40-50 percent off. Then I get them from anywhere, Menards, K-Mart (RIP), Ace Hardware. I also have a source who gives me some small evergreen trees every year, just because she likes me and thinks I'm cute.
This year I'm going heavy tomatoes and peppers again. Looking to expand the perennial plantings and another succulent area. I also anticipate going to war with voles and rabbits, as they seem to have overtaken the neighborhood despite the best efforts of my two dogs.
Looking forward to a good spring, plenty of rain, and heat when we need it. That perfect growing season seems to come about once every ten years, and we had that 2 years ago, yet I'm ever the optimist.