There are many professional bakers, but these can tend to be expensive so if you are on a tight budget for this part of your wedding, ask around friends and family. Someone usually knows at least one person that bakes.
For our wedding, we had a close friend make ours. We bought the ingredients and decorations and she baked and decorated it as our wedding present.
If you are having a professional make your cake, ask for samples before the day so that you are happy with the taste and texture which are both very important.
Discuss your requirements with them and give them as much detail as possible on the other aspects of your day.
Also, if you are having flowers on your cake, try to take in a sample of the colours of dresses etc so they can be easily matched.
You will also need to decide on what type of cake recipe you will have.
Fruit, sponge, plain, chocolate?
It is sometimes nice to go with both so your guests have a choice.
Then, finally, choose your decorations, icing and the most important cake topper. These can be comical or traditional and can be a defining talking point.