Since getting the new iPhone, I’ve been using OmniFocus for to manage all the things that I have to do. But the only downside with OmniFocus is that it’s Mac only – so if you’re using Windows or Linux you’re basically out of luck.
If you’re in this situation, I’d recommend you take a look at RememberTheMilk (RTM). RTM is an incredibly flexible time management system that’s capable of scaling from a single to-do list, all the way up to a complete, complex GTD-based system. It’s also got an API, which means that as well as working through your browser it can be access through other applications. And, as a post on the Remember The Milk Blog demonstrates, people are really putting some good work into nice little apps that work with the API.
They’re also working on a native iPhone app, which should give you access to your to do’s even when you’re out of signal range – although if you are in signal range, the iPhone web app is very good (winning an Apple Design Award at the last WWDC). There’s also native apps for syncing with BlackBerry or Windows Mobile to do lists, and Google Gears-based offline access for Firefox users.
One of the best thing about RTM is the shared to do lists. Say you have a list of things which need doing around the house. These can be shared with your partner, so that you can both see the full list – and share the work!
Most of the features of RTM are free, although you can optionally pay $25 per year for "pro" features like BlackBerry/Windows Mobile syncing. Given that this works out at less than $0.50 per week, I think that’s money well spent. When the native iPhone app comes out, I’ll definitely be taking another look.