For the past year I have been using Koodo's prepaid plan, which allows me to buy 1GB of data and use it until it is gone, with no expiration. They do the same with buying talk minutes. The downside is that they have a minimum monthly charge (about $13.50 when one factors in discounts for auto credit card payments and the like) that you need to pay (it does give you unlimited texts). This is in comparison to SpeakOut which only has a ~$2 911 fee each month.
For my useage, data and voice calls end up being cheaper by just a few bucks each month to go with Koodo compared to SpeakOut, but not amazingly so. We still have our "extra" family cell phone set up on SO.