Well, constantly changing everything in my GTD setup was a little bit of an exaggeration. I have a few steady items there:
For email, after trying many alternatives in the beginning, I use Mozilla Thunderbird for maybe 7 years now.
I have my physical inbox/reading material trays.
The "paper" part of my setup is completed with my filing cabinet, which I prune once a year. I use a free form organizer called MyInfo for my digital filing system (mostly interesting articles from the Internet, which I am afraid will be "lost" when they are deleted from the web site, but also research and ideas for future projects).
I will definitely check out the thesecretweapon.org. I already have Evernote on my phone, so I will give it a try. It sounds like some digital version of the Hipster PDA, which I also used in the past.