I use Alton Brown's recipe for an orange juice brine, simple and cheap, and really does a nice job. I've done breasts 7 times now with it, and every time they were excellent. You can find it on foodnetwork.com...or right below:
Alton Brown Orange Juice Brine
1 qt vegetable stock, chilled (regular, not low sodium - that's important)
1/2 cup kosher salt
1/4 cup dark brown sugar
1 tsp black peppercorns (I usually use more like 1 tbsp, but I like pepper)
2 bay leaves
1 qt. orange juice, chilled
2 qts. ice water
Bring 2 cups of the stock, the salt, brown sugar, peppercorns, and bay leaves to a boil. Dissolve the sugar and salt, and cut the fire. Add in the remaining stock, orange juice, and ice water. Once the brine has cooled to 40F or under, add the meat and keep in a cold place (under 40F). Brine for 8-48 hours.
I use more pepper and more bay leaves, but otherwise I keep it the same, and it is very tasty and makes a beautifully juicy bird. I've soaked for 24 hours and 48 hours, I would stick with 24, gets a hair orangy after 48, not a bad taste, just odd I think.