The biggest problem in finding companions is the size issue. At a foot in length your alligator lizard is not done growing. Depending on what subspecies it is it could get considerably larger. This means that any cage mates you select would need to be large enough to not be consumed. For this reason I don't think that the smaller western skink would be a good choice.
All the other lizards are going to like it a bit drier than your alligator lizard. Spiny lizards (Sceloporus sp)like the western fence lizard would be your next best bet. They are heavy baskers, however, so you would need to provide a UV light and a strong basking light. You would also need to keep humidity levels low. Because of their rough scales, mites are common and very difficult to find on spiny lizards so you would risk infecting your alligator lizard.
Most of the other native lizard species are restricted to desert environments so they would require high heat, bright light, lots of UV and minimal humidity. None of which would appeal to your alligator lizard. Therefore, I think that a Gilbert's skink because of its large size and similar habitat pereferences would be the best choice if you want to add a different species.
Mites are about the size of a grain of pepper and they reside under the scales of reptiles and feed off the blood of their hosts. Because of their smal size and secretive nature, mites often go unnoticed until they have reached dangerous levels. Good places to look for mites are in the ears, behind the limbs, in the corner of the mouth, and around the vent. Also watch your lizard carefully and see if you see anything crawling on it. Abraided or roughened scales or rubbing on cage furnishings are some warning signs to look for.
Sexing alligator lizards is difficult. Mature males will have broader more triangular heads than females. If your lizard is still pretty fiesty you can grab it roughly and flip it over, males will sometimes evert a hemipenis while trying to poop on you (lizards that have been habituated to handing usually won't oblige).
Southern alligator lizards come in a wide array of colors. Look in the kingsnake alligator lizard photo gallery for examples. So, it is possible to stick with alligator lizards and still "spice up" your tank.
For information on southern alligator lizard subspecies and other lizard species check out www.californiaherps.com. Western Reptiles and Amphibians, Third Edition by Robert C. Stebbins is also an excellent reference.
If you know the location that your lizard originated from, I would probabley be able to tell you what subspecies you have.
-Alice