Heather,
What a great opportunity for you!
I have done lots of booths over the years at baby fairs and such, and starting this Saturday my little town is starting a Sat. market once a month thru Oct. and I'm going to have a booth there. I'm specifically going to advertise my childbirth services for classes and doula service.
I have learned over the years that less is more...in other words my first couple booths I went over board on what I put out in the way of flyers, brochures, etc. Think of yourself at the fair or someplace with booths where you wander thru and start picking up everything off of the tables, well at least I do!

Then I get home and look at it all and feel overwhelmed, and most goes in the trash.
So, keep it simple. If you have brochures I would personally go with those over business cards...they are bigger and not lost as easily and will have more info on you and your service.
You might consider getting one of those poster boards that open out and fill it with pictures of you and clients, and maybe on one side write the benefits of using a doula for birth...people love to see pictures.
A basket with something free to take is always good and draws people over.
Put out a handout on doulas and the benefits with your name and # on it or your business card stapled to it...then they have both your brochure and business card, but the business card isn't just floating around by itself.
Consider putting out your doula 'tools' such as a rice sock, massage tool if you use one, massage oils/lotion that you use, essential oils, etc. Then you can get a conversation going as to how you would use these during labor and birth...gets moms thinking about their options.
And the basket for the prize drawing...how about a box of red raspberry leaf tea, a mug with something to do about birth (if you can get it in time), preggie pops, a copy of a book...maybe a breastfeeding book, a rice sock...these are easy to make, some nice lotion, etc.
And on your slips that the moms fill out for the drawing have a box they can check off if they would like more info about your services. Then within a week or two at the latest either call or mail out info to them. I myself am funny about having people call me about their services, it feels like a sales call, so I would be more apt to have a letter written up that you can mail out and then enclose your business card. You could also include at that time a discount for your services if you wanted and make it good through a certain time.
The discussion topic should include info about yourself, how you got started and why, and what a doula does. I wouldn't concentrate so much on the benefits or stats of having a doula, but maybe talk more about how a doula can help a mom through various situations...give examples from births you've been at...women love a birth story so share if you have any. Show your 'tools' you brought and explain how you've used or would use each one. Demonstrate the birth ball and positions that be used with it and how each can help a laboring mom. Explain how scents can help a woman stay calm during labor or give her a boost if she is getting tired or help any nausea she may experience.
Anyway, just some ideas. Let us know how it goes.
Amy