creating an online to-do list

[modelamac]

Notes in iCloud on Lion & ML. They will show up in Notes.app on all Macs using that Apple ID for iCloud. I do this.

[Ken Sp.]

Reminders in Mountain Lion and iOS devices.

[sekker]

We've started using Astrid for this after using google docs.

They just released an iPad app, too. Looks nice.

[Chakravartin]

Ken Sp. wrote:
Reminders in Mountain Lion and iOS devices.

...via iCloud.

Seconded.

The problem with syncing Reminders, tho is that alarms end up going off on all of your Apple devices simultaneously and that can get annoying.

[StingMe]

http://www.toodledo.com/ is free...

[Felix]

BusyCal