My Lowes sells Burpee and I haven't had very much luck with their seeds. In fact, I've had such bad luck, I won't buy Burpee again.

My personal favorite is Johnny's Seeds. Their price is a little higher than others but they have an awesome catalog and I get almost 100% germination and healthy plants from their seeds. Lots of people on the forum recommend FedCo, though I don't have personal experience there. I'm sure others will chime in with more recommendations.

I don't know where you are regionally. I recently got a recommendation for a couple seed companies housed in the Pacific Northwest that carry varieties that supposedly do well in my area. I'd already bought all this year's seeds, so I haven't tried them yet. The point being, finding a seed company in your area is another choice, as they might favor varieties that do well in your climate. It's not a requirement. I'm in California, Johnny's is in Maine and I still have good luck with their seeds. But I am curious to try some growers closer to home and compare my results.

I buy mine from Westcoast seeds (www.westcoastseeds.com). I've been buying from them from years, I've never seen such a great germination rate from a pack of seeds as I do from theirs. They're a Canadian company, not sure about shipping to the US (I know I can't send seeds to my in-laws in NYC, border issues).

I was in walmart the other day, and they have their seeds out. They carry ferry morse and american seed. The american seed is 20 cents a pack and I have always had pretty good success with them. I also have great success with ferry morse.

For online purchases there are several.

tradewindsfruitstore.com
rareseeds.com
sampleseeds.com
stokes.com
seedsaversexchange.com I always forget this one, I hope I put it in right!!

plus many more..