The one problem that I have with the familiar list is that some familiars can attack while others can not. Despite that big difference, the bonuses granted by these familiars are not very equal. I would think that familiars that can not attack should have slightly better bonuses or a different class of bonuses. For example, familiars that can attack grant skill bonuses while familiars that can't grant save bonuses or other (HP, Natural Armor, etc .). I'd also suggest that since bonuses to skills are +3, some familiars should give bonuses to skills that are +2/+2. For example, IMC, I will allow squirrel familiars. They are D sized creatures, have no attack, but will grant +2 Climb and +2 Balance skill checks.
Bertman