Three camps I've seen:
1. Hourly ($60–$120/hr, billed in 15-min blocks)
2. Flat fee per job type ($50 setup on anything custom)
3. Buried — design is "free" but the sign price is padded
Each has problems. Hourly scares customers, flat undercharges on revision-happy clients, buried trains people that design is worthless.
What's your system, and what do you do when revision #6 rolls in?