I've ordered seeds a very few times, only some kind of odd stuff. OR, some promotion/free shipping sort of thing. BUT, I did order seedless tomato sees the very first year they came out(Burpees) Seeds were $5 for 10 of them, only 4 germinated, and the tomatoes were just pitiful. They were good though, and definitely seedless. I think I ended up with around a $7 charge for sending 1 packet of 10 seeds!!
Mostly I grow the same old stuff as always, and save seeds from year to yer. I did enjoy Martins give-aways though, I probably planted and tried out 50 varieties of tomatoes.
I sometimes get the urge to buy seeds on EBAY, but honestly, you don't know what you're getting. The local seed&feed used to give me seeds for half price, and beans, corn, etc for a buck a pound, after the season was over. Worked for me, year old beans perform like new ones, but corn loses viability at the rate of about 33% a year, in my experience.