There are a number of options for bus transportation in and around Winnipeg:
Greyhound (1 800 661 8747) and Grey Goose are the major in-out bus companies in Winnipeg. You go from Winnipeg to practically everywhere in North America with Greyhound, which has several departures a day eastbound (towards Thunder Bay and Toronto) and westbound (to Regina and Saskatoon). Greyhound also acts as agent for Beaver Bus Lines, which has routes to Ft Gary, Selkirk and points north. The buses leave from the Mall Centre Bus Depot at 487 Portage Ave.
You can also charter a bus. This is great if you travel in a group (a company ski trip, for example). This makes sure that, if you're drinking, nobody is driving, and that everybody gets to your destination together.
By the way, if you're looking for the CHEAPEST way to get into town from the airport (all you backpackers and students), catch the Winnipeg Transit bus which runs every 20 minutes. Catch the Sargent No 15 bus and pay the $2.00 exact fare.
Find Local Bus Companies (charter & scheduled).