Is complicated, hardcore and expensive. It's not “shit” or something — it's just not for me.

Things ($50 Mac + $10 iPhone/iPod)

Is the coolest to-do app, really, but it's just a well-designed expensive app — I like cloud services more than Wi-Fi sync between a Mac and iOS devices (:

Is a promising web application focused on simplicity. Looks like it will be awesome… But I don't know anything about their iOS app and they can't send me a beta invite :(

EpicWin ($3)

Is an awesome iOS app which makes doing things fun by giving XP and loot — just like role-playing games. I don't like RPGs, but the idea is very good. The app totally lacks RTM sync — I don't like keeping all the tasks in my iPod, but that may be fine for you.

Remember The Milk ($25/year pro)

Is a cloud service (with awesome iOS and Android apps) which is not too simple or too hardcore. Well, maybe Things for iPhone is easier to use than RTM app (I mean, requires less clicks for doing, oh, things. Checking a task in Things - one tap. In RTM - swipe and tap). And it may have a better icon. But RTM pro subscription is cheap (yep, Things for Mac = 50$ = two years of RTM pro. I don't like big one-time payments, and you too, right?) and it is really cross-platform. I use it on my Mac (web version in Fluid), on my iPod touch, on my Linux netbook (with Getting Things Gnome!) and I even sync it with my WinMo phone. That's cool.