If your looking for an affordable idea, using your existing blinds, tint a 4 or 5" border around the edge of the window. I know, this sounds goofy but it works and it doesn't look that bad.

This isn't my idea, a client with a full wall of windows on the southern side put up mini blinds to block the light. So much light came through the outer edges the screen was washed out until 9:00 at night. He had a 5" 'border' installed. It actually worked!

The Total dark blinds are obviously the best aproach. It's all a matter of money!