I use Mindjet MindManager 8 to orchestrate all of my projects, and Gyronix Results Manager to sweep all my dozens and dozens of maps containing Next Actions into a single GTD dashboard. I find this makes the Weekly Review quite manageable. I also use Gyronix GyroQ as my quick capture tool, since it integrates directly with MM.
The whole affair takes a minute or two to generate the dashboard (which may be too long to wait for some, but I do have quite a large number of maps), but then I am completely confident that all tasks have been swept up wherever the individual map sits.
I have a Palm LifeDrive, and send my Next Actions to Microsoft Outlook for sync'ing to the handheld.
MindManager is great, I use it for brainstorming and for organising all my projects at work. Top level branches are for projects, and branches off those are NAs for those projects.
However, this is the only part of my GTD system that isn't mobile and I can only update on my work PC (or from home over my VPN, but that can be too much hassle). But being able to see all the projects I have on, along with their NAs, makes it worth it for me. It prints really nicely too, so if I'm heading off to a meeting or something where I'm likely going to have to wait for others or have some spare time, I'll just hit "print" and grab it on the way out the door.
I was told about MindManager by a learning specialist at my university a couple of months ago. I downloaded a free 30 day demo and then ended up buying the software after it expired. So far i've used it primarily for lecture summarys. Recently I've started to integrate it into the whole GTD system - preparing to do lists, tasks, etc. I actually found out about David Allen's book and this site via Mindjets website. So its been a double bonus.
Overall i've found MindManger has been fantastic software - its neat software and actually fun to use. The user interface is fairly well laid out. Although, MindManager 8 has decided to mimic the terrible interface of Office 2007. Despite that, MindManager has actually laid out their interface in a logical fashion, something Microsoft could learn from. Overall, its very easy to use software that is quite stable and customer service has been very good. I would highly recommend it.
Take a look at NovaMind. They offer various versions (Platinum, Pro and Express) and one license is good for both the Mac and Windows versions. I like NovaMind's interface, and that they keep the Mac and Windows version in parity (a major fault in MindManger). They are releasing a new version (5) in September/October 2009. If you buy the current version, you get a free upgrade.