I'm going to plant some boxwoods in front of my house. I plan on keeping them small... about 20 inches from side to side. My flower bed is about 3 deep from the foundation to the grass. I'd also like to be able to plant some annuals in front of the boxwwods. How far should I plant the boxwoods from the house?

I wouldn't go any closer than 2 feet, even keeping them as small as you say. You need to have room for ventilation around them, both for your house and the boxwoods (so they don't get mildew). If you could, I'd go 4 feet out for the bed, and about 2 1/2 feet for the boxwoods to give more room for annuals. Good luck.:)