Screw spending loads on a taxi with that damn meter running and do not even think of taking the train from Pearson to downtown Toronto (it takes roughly 90-120 minutes that way).
Jump on board the Airport Express bus that is located right outside the airport and stops off at numerous hotels in Toronto. Takes about 20-35 minutes depending on where you are staying.
The bus is new and equipped with free Wi-Fi. My brother and I purchased two round trip tickets for $62 Canadian or $50 US. When you think about it, a cab could cost that much one way and offers no Wi-Fi and probably smells funny.
The bus was constantly outside of my hotel's lobby, so it is very convenient and worth the investment. Clean, quick and affordable.