In one of the podcasts, someone on the design team mentioned that they were trying to come up with a solution for familiars and animal companions that wasn't just an easily forgotten skill bonus but that also doesn't effectively result in the player running two complete characters. My guess is we won't see them until PHB2.
All my PC wizards had the option of taking a 'magic-y' feat instead of a familiar (wpn focus- ray, item creation, still spell, etc). Not one had a familiar, they just are too fragile. Useful, yes, but they die. A lot.
If you are a short a 5th and don't want to scale adventures: Assume racial stats of a human or halfling, throw on generic fluffy, scaley, furry outside, and add powers to flavour then serve.
What about a minion-like entity. Goes down after one hit, but isn't dead. The 'owner' can 'rez' it w/ using one of their own healing surges w/in 5 minutes of its fall.