I've taken my car into Mexico multiple times from the United States, on a Tourist visa. Is it possible to take more than one car registered to me at the same time (obviously with a second driver)?
From the US Consulate:
Tourists to Mexico wishing to travel beyond the border zone with their car must obtain a temporary import permit or risk having their car confiscated by Mexican customs officials.
To acquire a permit, one must submit evidence of citizenship, title for the car, a car registration certificate and a driver's license to a Banjercito branch located at a Mexican Customs office at the port of entry, and pay a processing fee.
Mexican law also requires the posting of a bond at a Banjercito office to guarantee the departure of the car from Mexico within a time period determined at the time of the application. For this purpose, American Express, Visa or MasterCard credit card holders will be asked to provide credit card information; others will need to make a cash deposit of between $200 and $400, depending on the age of the car. Please do not forget to ask for your receipt from Banjército.
In order to recover this bond or avoid credit card charges, travelers must return to any Mexican Customs office immediately prior to departing Mexico. Disregard any advice, official or unofficial, that vehicle permits can be obtained at checkpoints in the interior of Mexico. Avoid individuals outside vehicle permit offices offering to obtain the permits without waiting in line.
If the proper permit cannot be obtained at the Banjercito branch at the port of entry, do not proceed to the interior where travelers may be incarcerated, fined and/or have their vehicle seized at immigration/customs checkpoints.
So it sounds really like as long as you have the ownership papers and registration, it doesn't matter how many cars in your convoy :D
To add to Mark Mayo's Answer.
There is no limit on the number of cars. If you don't own the car you need a letter from who does. IE if the car is leased you need a letter from the leasing company; If the Bank still owns the car, you need a letter from the bank; etc. The letter needs to say you are authorized to take the vehicle into Mexico. Since you, (the owner), would be with them it should be easier, but you may still want to write the letter for them to keep in the car.
I would refer to Mark's quotation for requirements and add, If you don't have a tourist permit you can not pass checkpoints. The tourist permits can not be obtained at checkpoints. You also need to insure vehicles.
This information comes from Instant Mexico Auto Insurance, they insure vehicles for groups of people involved in international off road racing, and pit stop crews are often driving cars that all belong to the Motor-sporting company.