Heather, be careful of the 'free compost' from horse farms. Horse manure can be very strong, both in smell and in nitrogen content that releases very quickly and can burn plants. If it's composted enough, usually at least a year, then it doesn't smell much and is excellent soil amendment. But most likely what you get "free" from Craig's List isn't going to have been composted properly at all.
Here in Sarasota County, our landfill makes excellent compost that is also free. You just have to go get it. (you'd have to go get it from the horse farms, too, I imagine) So check with your local landfill and see if they have a composting program.
That being said, for a north facing bed where you'll have low-maintenance things growing, you don't need fabulous soil. Bromeliads would be my first choice for that spot, and they come in a dazzling array of shapes and colors. Check out the Bromeliads thread in the Tropicals forum to see some great pictures. They are a very carefree plant, too.
As chellie mentioned, Coleus are another carefree type of shade lovers that would suit your flower bed very well. They require a little more water than the bromeliads but not much. I think we have a whole forum dedicated to Coleus, so you should have a look at the pictures over there, too.
