Remember the Milk is my go-to to-do list maker, and more. I use it for meal planning, reminders for chores and birthdays and more. Being able to use the web app, iPhone app, Gmail or Gcalendar app make it versatile and accessible.

We just launched a task management app called Helium that you may be interested in checking out. It is free on the iPhone and integrates with your email and Evernote. It also has a Windows and Mac desktop client that syncs with the iPhone (requires subscription).

You can watch a tutorial here: www.heliumnow.com.

Droplist is pretty sweet since it syncs to your Dropbox and it's pretty easy and fun to use: http://www.bloomingsoft.com/droplist/

GoTasks is a great (and free) Google Tasks based task manager, nice option set, and meaningful updates.

I have tried a lot of these sorts of apps.

I keep coming back to Things.

http://culturedcode.com/things/iphone/

I am currently using OmniFocus

http://www.omnigroup.com/products/omnifocus_for_iphone/

OmniFocus is very full featured, and has much more graceful syncing at the moment, but the authors of Things are working on syncing now.

I just use the Calendar App on the iPhone. Are there any reasons I should consider using something else? It syncs with my Macbook and does the job for me.

After trying out a handful of sync'd apps to try and get my wife and me on the same page, we settled on the simplicity of Zenbe lists. I ended up using my account (set up through the app's site) for both of us, and now our iPhones and iPads are all linked. Now I don't have excuse when I forget to pick up those few items from the store, and we can keep track of home projects together without spending a lot of time on the phone (or SMS).

Try the freebie lite version of as many as you can get your hands on. Tasks managers work better for different people.

I thought I wanted one with lots of bells and whistles, but after trying out a dozen my favorite was a SUPER simple text list barely more complicated that using notes.

It helps to figure out what you need most out of the manager. In my case, I needed speed - if my task couldn't be entered completely in five seconds, I realized I just wouldn't put it in, or I'd think "I'll do it later" and I would, of course, forget.

i've been a pretty solid appigo ToDo user for a while. i love that you can do recurring tasks and schedule accurate reminders for a specific time on a day. it can break things down into projects, or tags or all that jazz. for more simple listmaking i would have to agree that it is hard to find anything more solid than TeuxDeux

things seems great and all... but its REALLY expensive, especially if you want to sync across multiple devices.

I second the vote for ToDo, and for the same reason as aneelee: repeating tasks! That was the feature I really wanted that was missing from other task management options like Google Tasks and TeuxDeux

I'm currently using Wunderlist and it's the first one that I've actually kept up using. Once I started using it, I became much more productive.

Most of these seem to have free or demo versions that you can try out before you buy. Try a few and see what you like. These tools are only useful if you actually use them. An app can have all the bells and whistles, but if you don't use it on a regular basis, none of that matters.

I've been using TeuxDeux for a while, and I really like it. It's simple, uncluttered, and it looks pretty. I don't really need a bunch of complicated features, like in some of the other task manager apps, so this works for me.

I have been using Awesome Note since I got my iPod touch in 2009. I like that I can make folders according to topic and then put individual notes in those folders. You can select it to be just a note or a to do, which allows to set due dates and reminders.

I use this app to keep my to do lists, store random thoughts and ideas about just about everything. I like that I can password protect some of the folders and not others, so I can feel safe in keeping some info private when my friend's 3 year old is playing with my iPod.

I like TeuxDeux, but since I started using Wonderlist, I haven't gone back. It's a great piece of software, it's beautiful, and it's designed by the great team at 6WunderKinder.

@Kaete - I'm with you, speed is critical. I'd call that "comfort and reliability" of an app. Things and Omnifocus are $$$, but will ultimately pay off if you enjoy using them. Remember, you'll be using this app a LOT.

For Mac, I recommend "The Hit List" It's a Mac only application (not available iPod/iPhone/iPad yet! Very frustrating.). It has a small but happy following and is perfect for me. Speedy, project-oriented, keyboard-friendly (I don't need to use the mouse!), has a quick-entry window (via keyboard shortcut), etc... I'm suffering for a mobile version, but until then it's a great application.

Things, Things and Things... and it works really well while reading David Allen's "Getting Things Done" - this has changed my life and work. I am not perfect yet but way better about Task Managing than I used to be with my phone, mac and this book.

For tasks I use Wunderlist. It's free, multi-platform, uncomplicated, elegant and syncs quickly.

For grocery lists I use GeeTasks (google tasks), but only because I can fit more items on a screen and I like having it completely separate.

I'd recommend Done - it's a nice middleweight app. Not overkill like Things or too simple like some of the free options. Check it out:
http://itunes.apple.com/gb/app/done/id300799754?mt=8

I use Toodledo. Whether you're using it as a GTD system or just simply for to do lists, it's very simple and flexible. I use the iPhone app and web version and easily sync over wifi. I've tried RTM, Evernote and a slew of others, but none were working for me. Once I tried Toodledo for the first time about a year ago, I stuck with it and use it religiously.

I love ToDo. It's been my personal to-do list for r about a year now.

It doesn't do all the things I need professionally, however, so I use OmniFocus for work.

I was a Things user for a while, but I didn't love it.