I think you need a car. It totally depends on the location of where you are staying, but it will definitely be easier to access the most beautiful beaches by car.

You can manage in St. John's without a car. You will be limiting yourself and not getting a good feel of Newfoundland, but then again you only have three days. I recommend you find yourself a b&b in the vicinity of Gower Street (don't confuse with New Gower) or one of the other streets in that vicinity. We stayed at a b&b called something like Bonne Esperence. It was very nice but may now be over your $$ as it was back in 2002. There is another called something Wit which I understand is very good, plus I met people who liked the Roses. If you stay in the vicinity of Gower Street you can easily walk to downtown or out to the Battery and up to Signal Hill and to the Geo Centre or over to Quidi Vidi. If you go out of town you may want to find a way to get to Cape Spear. I'm not sure what kind of transportation you can find there. You can also try renting a car for just a day - away from the airport - Enterprise or Rent a Wreck. Enterprise will give you a ride from your b&b. Hope this helps.

Thank you both for your suggestions.

I really like the idea of renting a car for just a day - thanks katrinasl - and thanks for suggesting to stay close to Gower Street, it does look like great location!

I have stayed at The Roses B&B a couple of times and love it there. It is withing walking distance of the downtown area, and also if you'd like to do a hike up to Signal Hill through the Battery, the Roses is very close to the Battery. You could easily fill 3 days without renting a car.

You could wander the downtown area for 1 day, hike up to Signal Hill another day, and then perhaps rent a car for 1 day and go out to Cape Spear , stopping at Petty Harbour along the way.