You have 4 main choices (5 when Disney starts the Magical Express service that wdwgoofeeee mentioned):
1. Rent a car. For a week of Economy class car, this will cost you roughly $120-$160. My personal preference because it gives the MAXIMUM flexibility - go where you want, when you want, and never wait for a bus.
2. Take Mears shuttle service. This is $27 per person, round-trip. Takes a long time and can be crowded, stops at multiple hotels.
3. Take a towncar service. Must be reserved in advance, cost is $80-$110 round-trip depending on company, holds up to 5 people (larger vehicles like vans and even limos available at higher cost). Best option for 4 people if you don't want to rent a car.
4. Take a taxi. Round-trip cost is about $90-$100.
5. Disney's Magical Express service, starting May 5, is a shuttle service provided by Disney (it's actually contracted out to Mears) that takes you from MCO to your Disney resort, included free with Disney vacation packages (I don't know if it's available for room-only packages). Luggage service included; your luggage will be delivered later by a different vehicle and dropped at your hotel (whether it goes to your room directly or you have to pick it up at Bell Services, I don't know).