The STM bus network consists of 169 daytime and 20 nighttime service routes. You can pay on the bus, but must have correct change.
Montreal's Metro is the best way to get around. It is made up of 68 stations spread out along four lines. It operates from around 05:30 - 01:00. You must buy ticket before attempting to go through the turnstiles.
Taxis (Cabs) can by hailed from the street. There are also designated taxi stands. Price is around $3.15 to start then $1.50 per Km. (Too book a taxi in advance see external link at bottom of page)
The commuter train system is handy for getting to suburbs and neighbouring towns. It is run by the Agence métropolitaine de transport (AMT). It's main stations are at the Montreal Central Station (Gare Central) and at Lucien L'Allier.
The same tickets are valid on both buses and the metro. A single ticket costs around $2.75, but you can buy a pack of six which costs $12. If using public transport a lot then you can make savings buying a 1 day Carte Touristique for $9, or 3 day pass for $17. You can also buy weekly passes at $19.25 and monthly at $66.25. Tickets can be purchased at all metro stations and Carte Touristique's at major stations like Berri-Uqam.
You can use your single STM ticket in order to transfer between the metro and STM bus. Currently, you need a transfer ticket (correspondance), which is obtained from one of the dispensing machines from your starting station. If you intend to transfer from bus to metro - request a transfer ticket from the driver. A transfer ticket lasts 90 minutes. (NOTE as of April 2008 a new type of ticket is becoming available, which allows you to transfer without having to obtain a transfer ticket - so please enquire at the station/driver).
STM Web Site
Metro Fan site