vendor gratuities? Whats customary/expected?

I'm trying to figure out my totals for my vendors with gratuites. Whats customary/expected? 15%? 20%? and do I tip everyone the same percentage?

I figure I have to tip:
photographer/videographer
DJ
Florist
reception hall (they stated a 20%gratuity will be included in final price)

anyone else??