I tend to wander from one toolkit for Getting Things Done (GTD) to another. (See http://www.kleinfelter.com/node/50 )

Here is a partial set of my current axioms:

1. Many incomplete projects
2. iPhone
3. Microsoft Outlook email at work
4. Moderate degree of 'lock-down' on client's network and computers, including don't-install policy and blocking of POP, SMTP and webmail
5. Business-supplied laptop running Windows XP
6. Desire not to over-fill my pockets or to carry a 'man-bag' (i.e. a purse)

What I'd like to accomplish:

1. Easy task capture
2. Ubiquitous access to read/write tasks even when offline
3. Linking of tasks to projects
4. Linking of projects to roles/values/goals
5. Automatic back-up (incl. local stash if data in the cloud)
6. Linked to a voice-to-task app such as Jott/Requall/Dial2Do
7. Not too much process friction

Why am I revisiting this topic? I just bought an iPhone and I'm thinking that things which were not possible before might be possible now.

Some random thoughts:

• Remember the Milk (RTM) talks to everyone (like Kermit)
• If it weren't for the Mac requirement, I'd probably use OmniFocus
• Toodledo has features that RTM doesn't. They don't support user-ordered lists.
• Requall has its own iPhone app, but it doesn't appear to categorize/tag. You can use "Places" but then you have to turn off Location awareness. It doesn't support ANY task sequencing.
• Location awareness in OmniFocus iPhone, ReQuall is a really cool idea
• My Life Organized is nice, but they don't have an iPhone app yet.
• Multiple iPhone apps synch with Toodledo
• Nozbe? $60 per year!
• RTM $25 per year to get iPhone app. (Their phone web UI
• Toodledo $0 per year. (They have a free web UI tailored to iPhone).
• Nozbe supports user-sequenced tasks via drag-and-drop; RTM sorts by priority or date; Todledoo sorts by a variety of fields.
• Near as I can tell there is no keyboard interface to Nozbe, and no way to search their help, and their wiki has nothing with the word "keyboard", and no way to search their forums
• Vitalist has drag-and-drop task ordering, and a decent keyboard interface. Vitalist has an iPhone web version which respects task ordering but cannot change it. They have a bona fide iPhone application (with synch) in beta. $0/50/100 per year (5/25/unlimited projects).  If their iPhone app is good, and I can get past $100 per year, Vitalist could be good at some point in the future.

• I thought about using Evernote, but you can't create a bullet on the iPhone app, and the iPhone app doesn't work offline. 
• Google Tasks supports multiple lists and user-controlled ordering.  The iPhone web interface is usable (but doesn't let you change task sequence).  You get to it via gmail.com and my employer blocks Gmail URLs, limiting its usefulness at work.
• Todoist supports user-sequenced tasks. (Click the Reorder link to enable it.)
  
• There are two iPhone apps (neither by Todoist). Update: I've been using Doings.  I'm pretty happy with Doings, except for the absence of search.  Doings provides very helpful and responsive support.
  
• Todoist is clearly a one man show.
  
• $0 or $36 per year.
  
• Frankly, it looks pretty good.
• The main drawback is that back-up requires some hackery. 
  
• Update: Another drawback -- no ability to search by text (except to backup to XML and search the XML with a text editor).