According to Microsoft Word-

The description of this question – Arial
Title of this question – Trebuchet MS (Bold)
The words “answer this question” – Rockwell
The words “observing members – Arial (Bold)
The words “Meta Question” – Rockwell
The words “Flag As…” – Arial (Underlined)
The words “Community Feed” – Rockwell
Your lurve score – Arial (Bold)
My answer – Arial

They appear to all be either the Arial, Rockwell, or Trebuchet MS fonts.

Rockwell! That’s the one I couldn’t remember… thanks @PhiNotPi!