https://www.muckrock.com/foi/list/
Before FOIAing an agency, I'll sometimes check MuckRock to get a better understanding of what to expect, including who to direct my letter to and an estimate of how long I might wait...or best of all, examples of precedent to use to bolster my legal standing ("On June 3, 2014, you fulfilled a similar request for James Smith via Muckrock").
Hell, you don't even have to be in the FOIA-writing mindset...just reading that list will give you a veritable shitton of ideas of the kinds of things about government that has piqued the interest of other reporters, private investigators, politicians, and hedge fund analysts. Analyzing the metadata alone would make for a very useful service.
Please please please check out their site if you're doing FOIAs. There is a cost, but its minimal, and worth it. They'll help you manage the FOIA process, and whatever records are returned become public on Muckrock's site.
Example: https://www.muckrock.com/foi/list/
Muckrock is awesome though.
E.g. The Pentagon will answer 100,000 requests per month, each individual will have a spot in the queue, when a request is received the next request from that individual is at (N requests * -1) in weight.
So:
X, Request 1, 0
N, Request 2, 0
Z, Request 3, 0
A, Request 5, 0
Q, Request 7, 0
X, Request 4, -1 [will be weighted 0 for next month]
X, Request 6, -2 [will be weighted -1 for next month]