I don't have much experience past in cars (which is only comfy if it's got a roomy back area)... Places that sound hottest to me are things like kitchen counters, sturdy tables... Cushy things need to be roomy for me, so beds are best for cushy.
Bathroom. We have shower sex or a lot of times on the rug just before one of us takes a shower sometimes. Occasionally in the living room, but with smaller children in the house it rarely happens out of rooms without doors that shut completely.