One regular location that I have noticed is adjacent to wall mounted refrigerated water fountains. (I guess they need electricity for maintenance.) In some places, like SDF, there is seating right next to the fountain. Otherwise, it's the floor.

This strategy also works in FLL, where there are outlets under the aquariums. (Again, for maintenance?) The only problem is the little kids running around. (If you haven't seen them, the aquariums are mounted around major support pillars, resulting in fish (and children) races.

A final generic suggestion, look on the wall around those ceiling mounted TVs. This has worked at both ORD and SDF.

In the old MDW, there were coffee pots with outlets in nearly every gate. The new gates seem to have outlets directly in the path of embarking and debarking passengers.

Of course, there're always the razor outlets in th washrooms.