Every so often I notice people mentioning "onesies", and I have a few from Abena (they call them "bodystockings").
Anyway, I don't know if there is a standard design, but the Abena ones are available with or without arms & legs. (See here: Bodystocking)
Since I'm in the mood for a poll, I thought I'd ask you all whether you prefer them with/without arms/legs. It's a multiple-choice poll, so if you like them both with arms AND without, you can vote for both.
Let polling commence!