1st - Scales of the Lizard (Complete Arcane)
2nd - Chameleon (Oriental) OR Scintillating Scales (Draconomicon)
3rd - Triceratops Charge (SpC)
4th - Wall of Scales (Races of the Dragon)
5th - Primal Speed (Dragon Magic)
6th - Dinosaur Stampede (SpC)
7th - Vipergout (Savage Species)
8th - Summon Monster VIII (lizards only)
9th - Shapechange (lizard forms only)
Unless someone can come up with better spells, this will be it after you decide on the 2nd level choice.