Mastery involves knowing the right tool for the job, and how best to use it. I am by no means a GTD master, but here is my "tool chain" in the hopes that others might share the different tools they use for the different jobs of GTD.
Sony ICD-502 voice recorder - used to capture while driving or walking
Pad of 8.5x11 paper with Pilot G02 blue ink pen, set of four multi-colored highlighters - used for general brainstorming, taking notes during meetings or on the phone, and for general note-taking throughout the day
Post-it notes - used to capture new things that should be acted upon the same day - they get posted to my monitor so they're almost literally in my face
Gyronix for eProductivity - this is to quickly note new tasks or projects directly into my electronic system
Evernote - this is for journaling and capturing notes on little research projects
Inbox - I have a standard stack of three, top is for In, middle is for pending (files I need now), bottom is for stuff that has been processed and must be filed (Out)
Email - Lotus Notes (with the eProductivity add-on)
Processing to "zero" happens at least once a week.
Email - for each email drag it to the appropriate category in eProductivity (next action, project, tickler, calendar)
Sony recorder - listen to all recordings and type actions and reminders into eProductivity
Inbox - empty every few days or at least once a week
Journal - I don't really "process" the stuff captured in my journal. Occasionally I will look back at previous entries to refresh my thinking about something.
eProductivity - contains projects, someday/maybe, next action, calendar, tickler
Blackberry - synchronized with Notes/eProductivity and used for reference on the road and automated reminders when away from computer
Google sync and Google calendar - I use google calendar for a lot of things, so my Notes calendar gets synced to it
wikidPad - write ups for my 50,000-20,000 ft outcomes, also for ad-hoc electronic reference notes
File folders and Brother labeller - reference files - hanging folders within which I put standard file folders
Western Digital External 500GB USB drive - all electronic reference files get stored on this little guy; it's bus-powered and very portable and high-capacity; backed up to drive at home
Where possible, automated reminders from Notes / Google calendar.
Weekly review in eproductivity using the weekly review coach
Daily review first thing in the morning to transfer daily to dos to paper list for the day
Pad of 8.5x11 paper and pen - start of day jot down the key tasks and outcomes for the day (from electronic system) and then work down the list, making notes as I go. Paper acts as a focusing tool for daily action. At end of day (or every couple of days) resynchronize as necessary back to electronic system - i.e. capture stuff from my paper to do list back into electronic (stuff that's longer term and can't be done immediately).