I think that Quantified Mind provides some high-value tests. So long as you're willing to sit down and take a test, you can get data on:

• Reaction Time
• Visuo-spacial memory
• Executive Function
• Working Memory
• Verbal learning
• Motor function

Also, looking at what Gwern tracks, it seems helpful to have long-run data on subjective mood and energy. I randomly sample myself on that with PACO. PACO can allow you to poll yourself on any kind of thing you can imagine, like whether you're sitting, standing, or walking, or whether you're in public or private.

Edit: Added detail on QM.