Your catering contract will include gratuity for the waitstaff and it will usually be somewhere between 18 - 25%. This fee is not negotiable and since waiters, bussers and bartenders work for tips it would be rude, in my opinion, to try and cheat these workers. But when it comes to other wedding vendors my views on tipping may vary from others in the industry.
The hair and makeup artist should be tipped if they work for a salon and are not independent contractors, meaning they are not self-employed. The same for drivers.
I do not think you need to tip the florist, band, photographer, videographer, officiant (you will probably pay him/her a fee), baker, DJ and wedding planner. Valets are similar to waiters and their gratuity is probably included in their contract.
For your wedding planner, you may want to buy a token gift if you’ve been working with him or her for your entire engagement.
Of course do what you think is right and if I missed a vendor comment or email me and I put in my two cents.
And while a gratuity may not be necessary it’s always a good idea to write a thank-you note.
UPDATE: Of course if you think the band, DJ, wedding planner, etc... did an amazing job you can give them an extra few bucks -- the total amount is up to you but $50 or $100 is probably average per person.