This is a frequent question on many forums.
The exchange rate today for US dollars is one US $1 for 19.95 pesos. (Very weak peso)
One Canadian dollar 15.49 pesos
One Euro 23.48 pesos
One British pound 26.87 pesos
What to bring? US dollars and MX pesos are widely accepted but you will get much better value if you use pesos as you do not leave the exchange up to your vendor or taxi driver. Taxi drivers especially are known to give bad exchange rates so if you have access to them bring pesos in 20 & 50 pesos bills.
Never use foreign coins( useless) or torn bills.
Any more questions just ask.