So many different ones, but the ones I still play include:
Ski Safari (doubler; bought the game when it was premium)
Pocket God: Ooga Jump (doubler; bought the game when it was premium)
Jetpack Joyride (doubler; will buy the sleigh as soon as I get new iTunes cards)
Sonic Dash (doubler; bought the game when it was premium)
Temple Run 2 (doubler)
Flick Kick Football Legends (cheapest IAP to disable ads)
Nimble Quest (doubler)
I don't play it anymore, but I also bought every single table in Zen Pinball (I got rid of my iPad, and I hate playing it on the iPhone). And I've also done doublers or other IAP in premium stuff.
Cannot remember names right now, but basically everything where I play for more than 10 hours gets some money from me (usually 5+€) , provided it's not a blatant cashgrab (Dungeon Hunter 4, looking at you).
In any case, that's only a handful of games for me, as there are enough high-quality fullprice games out there; and my free time is very limited, so I spend it in my genre (real RPGs like Avernum or Baldur's Gate, strategy like XCom) mostly.
Bought the big 50€ pack at Ravenmark:Mercenaries launch to support the devs, and like 10€ to get all ships in Strikewing:Raptor Rising, also to support the devs.
Full game unlocks, additional content, etc, I do not count as F2P. E.g. the Kingturn games, or Warhammer Quest.
The only F2P game I can remember buying an in-app purchase for is Clay Jam. I bought a permanent power-up upgrade specifically BECAUSE IAPs aren't necessary to advance the game -- I just wanted to support the devs in some small way. It's the most uncynical "freemium" game I can think of. <3