Go with MLO (my favourite tool)
I'd wholeheartedly recommend MLO
I suffer from "chasing the newest shiny tool out there that will solve all my GTD problems"-itis - invariably, they don't, and I've ended up returning to MLO more times than I care to mention.
I had a quick look, and you can do the 'Effort list' you mentioned - you need to set up a specific view for it. I can send you details if you go ahead with MLO - just let me know.
MLO has been a godsend for me, given its flexibility. There are still a few shortcomings, but having said that, there is an iPad App on the way, as well as improvements to the desktop version.
Afraid I can't comment on the Android App as I'm an iPhone lad - but my understanding from the little I've seen is that the Android App is better than the iPhone App.
Also - I should mention - I have no affiliation with the development team, just a very happy user :)
Hope this Helps....
Also tried many and the winner is...
I also tried many other apps for GTD including MLO, Vitalist, RTM, Evernote but I always had the same problem: I had to use separate apps for email, calendar, list manager and reference. It was hard to keep these all together, however these are all belong to my productivity workflow.
Being tired of it, I read through the Outlook implementation guide whitepaper produced by David Allen Company and spent some hours on implementing it.
Now, Outlook 2010 have all the things I need. I tweaked it with some smart macros found on the web (for archiving mail, creating task or waiting for from a mail - these are all supported with keyboard shortcuts). I also started to use OneNote for keeping project support and reference which seemlessly integrates into Outlook.
To have it always with me, I use the Chromatic Dragon software to sync all the tasks to Toodledo and a Google app to sync calendar to Gcal. From this point, I can get to my system from almost any mobile or desktop devices. Even Onenote has web and mobile apps to which it syncs nicely.
If you want to add some creative support for implementing the natural planning model for projects via super flexible mindmaps, Mindjet's MindManager or Xmind with Xmindlook add-on can be integrated to it also with decent task syncing capabilities.
So, keep on testing what suits for you the best, I hope I could add some considerable points to that.
As a bottomline, I always prefer smartphones with physical qwerty keyboard as it is much more convinient for reviewing or capturing new ideas on the go - or eventually write a forum post while sitting in the garden on a sunny Sunday afternoon :-)
Be careful what you ask for
robs23, I just gotta say that if your mind is made up that you have to have dependencies in your software, then you may not be receptive to the main messages of gtd at this time. One of the main ideas of gtd is to get stuff out our heads, sure, but 90%+ of projects just need a next action. Most people who successfully practice gtd don't use software that formally supports dependencies, just as most don't use priorities much. At it happens, I am using software that does support project outlines, dependencies, flags, and a lot of cool stuff [OmniFocus], but I spent a long time learning to use those features in a simple, effective way, and an even longer time resisting the simple disciplines of gtd that are tool-agnostic. Of course, your situation may be completely different from mine.