As noted by John Gruber and Living with Mac, the iPhone doesn't currently appear to have built-in support for "to-dos" -- even the modest task support that's built-in to OS X's iCal. :-(

While this is difficult for me to understand (I know it's something I'd expect in even a Gen 1 smart phone), it's cool to see that web- and Mac-based developers are stepping up to the plate in the absence.

A few of the apps I've seen so far (and in varying states of reality and vapor):

• Ta-da Lists - The wonderfully simple app from 37 Signals has been quickly adapted into a lovely iPhone-friendly interface.
• do.Oh - Boy genius, Ben Brown, has whipped together a snazzy looking chunk of func for basic task and list management.
• @task for iPhone - Looks pretty sexy, but the site is light on info, pricing, and availability (without filling in a goofy form).
• Nozbe -- Announced, but I haven't seen what this looks like yet. Supposedly coming this week.
• OmniFocus - (Disclosure: I contribute to this project) - Although it's still in very early and buggy development (even for an Alpha), our friends at OmniGroup were quick to add an HTML front-end to context view that can be served over your Mac.

I'm sure there are others that I'm missing (which I hope you'll share in comments), and I know this is something that's a priority for a lot of you proud new iPhone owners: What are you using to manage actions from your iPhone? What would a home run look like in terms of future, built-in to-do support for the iPhone?