Besides the obvious Starbucks choice[1], my personal recommendation: PieFace. Their cafes are throughout midtown and have good coffee + outlets + seating + great food (Australian meat pies and pastries).

They claim to have wifi but I usually use my phone's hotspot.

1 - for those who want (need) Starbucks, the one at 39th and 8th Avenue has tons of room on the second floor seating area.