Unfortunately, Blackscale Lizardfolk are monstrous humanoids, so you can't change into them using alter self.
Humanoid:
[utility/combat] Avariel are nice for their flight, since alter self is one level lower and longer lasting than fly. You could also get out of reach of melee and cast with impunity if you're in the air. (Raptoran flight requires 5HD, so it's not as good of a choice yet.)
[utility] Skulks. They give huge bonuses to Hide and Move Silently, so this is a great form if you want to sneak around.
[combat] Tren. +8 natural armor, a 30 foot land speed, and 40 foot swim.
For your familiar: (sharing spells is caring spells. Or something.)
[utility/combat] Beguiler. Multiattack as a bonus feat and a bite/claw/claw/weapon attack routine mean that this form is good for delivering touch spells (my favorite touch spell for use with natural weapons is parching touch). Or dealing a lot of damage, if you have an optimized IC/DFI bard around. Also have a +8 racial hide bonus for sneaking. It's a shame a sorcerer is unlikely to have any ranks in stealth skills. Sadly, alter self doesn't give your familiar access to the beguiler's always-on true seeing. You can also take these as cohorts or familiars and they are super cool. (I am hugely biased here.)
If you somehow become a dragon (dragonwrought kobold is an excellent racial choice for a sorcerer):
[utility/combat] Wyrmling Shadow Dragon. +7 natural armor, fly speed (capped at 120 by alter self), and they can cast. This form is Tiny, so it's for flying up near the ceiling or into the sky and raining magical death down on people, not melee.
Trollshape: The worst part is that you lose your class features, which means you can't cast. Technically speaking, you can't have a familiar either, which utterly boggles the mind. This (and similar spells, like body of war) are best cast on your familiar, IMO.
This is by no means comprehensive, but I hope you found it useful.
