Delete old revisions and optimize your WordPress database.
This halved the size of my database.
Settings are under Settings > Optimize Database
Delete revisions older than [x]  day(s)
Maximum number of - most recent - revisions to keep per post / page [x] 
Delete trashed items [x]
Delete spammed items [_]
Delete unused tags [x]
Delete transients [DELETE ALL TRANSIENTS]
Delete pingbacks and trackbacks [_]
Optimize InnoDB tables too [x]
Keep a log [_]
Scheduler [run optimization DAILY]
Time [0:00 hrs]
Show '1-click' link in Admin Bar [_]
Show an icon in the Admin Menu [_]