I smoke my own jerky all the time. while not as simple as just buying it, its pretty satisfying to do yourself. the best meat i've found recently was a "bag-o-meat" i got a couple days ago for about $1.70 per lb. (aprox 11lbs.) its the same cut they use for carne asada. big chunk of lean meat with a good grain. they had a bunch of presliced stuff out for cinco de mayo so i asked the butcher if there was any left uncut.
for marinade i just grab whatevers around the house that sounds good. teriyaki sauce or soy sauce for a base, and then whatever random marinades i've got in the fridge, ginger, garlic, sugar or molasas, peppers, whatever. a little liquid smoke if you're going to use a dehydrator or the oven to cure it, and it pretty much always comes out good. (except for the occasional incineration). however there's also hundreds of marinades for jerky all over the net in various cooking sites ect. if you don't want to just wing it.