Another one of my favorites. Child's calculator similar to Little Professor but with wizard rather than owl on face. TI made calculators for sale under other names, including Radio Shack. These are more difficult to locate than the TI versions. The Montgomery Ward calculators are especially fascinating as they are not obvious clones yet can be identified as related to specific TI models.
Some models are difficult to find in good condition.
Other models, such as the 2500 and 2550, are usually in quite nice condition. Last issue, I mentioned a Longines-Symphonette similar to the TI 2500B. I have since discovered one similar to the early version of the 2500. It has the same green case color as the other. Finally, TI calculators often have a data code stamped on the back.