If you're not familiar with Everything, it is the future of online publications.
They identify the best writers online discussing work, productivity, and finance, and add them to their list of publications that you get access to for one monthly fee.
The best tool I've found for monitoring sleep quality and recovery.
Extremely useful for seeing how lifestyle changes are affecting my sleep and for giving me rapid feedback on what's aiding or hurting my physical recovery.
One common thread among all the really successful and productive people I know is they have a "systems mindset."
As soon as they do the same thing more than a few times, and that thing is not $1,000 per hour work, they start to think about ways to automate or systematize or delegate it so they can focus on something else.
Sometimes this manifests in small ways: I type in my email all the time, so I set up a hotkey in TextExpander to type my email in 3 characters instead of 20.
If you pay $3-5 a day for a bit of caffeine to help you be more productive why would you spend anything less than $100+ per month on your key productivity tools