First off...how the [censored] did you get 100,000 miles of free oil changes?? Jesus! That's a deal and a half!
I received two "free oil changes" with my Silverado. I had to wait two hours for the first one so they could throw who knows what in there. Two hours. Fell asleep in the waiting area at the dealer. I don't think I'll go back for my other "free" one.
As for the oil, any brand name off the shelf oil at Walmart will do (and you really can't beat their prices). Shell Rotella gas truck oil has a rebate goi on until the end of the year...you'll end up paying around $2 a quart, you can't really beat that. And Wally worlds Super Tech is good and cheap too. And of course you can always get the lowest price on Mobil, Pennzoil, Castrol, Quaker State, right there at Walmart. And I hate Walmart - can't stand the place - I've been known to leave my carriage right in the store when I pull up to the register and there's a line a mile long because they don't want to employ anyone anymore.