If you are looking for ink jet transfers for IRON-ON, I'd recommend the Avery brand (that you can buy at Office Suppy stores). Make sure you apply HEAVY, EVEN pressure with the iron to affix the transfer properly, and also make sure you trim the excess around your design before ironing.
I would not recommend you actually sell iron-on shirts, though. You might use them as a prototype or to give to friends, but the lower quality and consistency just isn't something you should be selling IMO. If you really want to sell some shirts before you can get your own press, you might try a fulfillment service instead.