Tax information would be HUGE. I would also like to see an API for general government records.
For example, if we had voting records, we could finally stop hearing all this "but you voted on -----" "no I didn't go back and check the record" "no look you voted on ----- which is basically the same" "shut up I served in the war" "yay war" stuff every election. We could just look it up and say "hey look you did". The Times "Congress API" is on its way to this, but last I checked, all it had was the attendance records.
For example, if we had voting records, we could finally stop hearing all this "but you voted on -----" "no I didn't go back and check the record" "no look you voted on ----- which is basically the same" "shut up I served in the war" "yay war" stuff every election. We could just look it up and say "hey look you did". The Times "Congress API" is on its way to this, but last I checked, all it had was the attendance records.