Does anyone know where the best rates of exchange can be found in Madrid? Is it a bank, or the airport, or anywhere else? (somewhere trustworthy obviously!)

Banks generally have the best rates. Hotels and the airport tend to be more expensive. However, I preferred to withdraw money from ATMs or use credit cards because I found the exchange rate to be better than what I could get exchanging the money myself. I ended up taking all my traveller's checks back home with me for that very reason.

I changed money at the airport, train station, and one store, and was the same rate of 171 pesetas per dollar. One Sunday where almost all the change sites were close the onlyone I founded offered 150 per dollar.
I used money for small things, for almost everything I used my credit card, once back home when I got my bank statement making calculations the rate was 180 per dollar.

Rafael