Most FloristWare users want to take advantage of the advanced e-mail marketing features contained in the software. Unfortunately in order to take advantage of these features you first need to have customer e-mail addresses on file.
So, the process of e-mail marketing typically begins with the process of collecting e-mail addresses. This is something that is usually best done on an ongoing basis - each time you make a sale or take an order you should be collecting (or confirming) the customer's e-mail address.
I think you always have to look at is a little negotiation. The customer has something you want (the e-mail address) but - given that most people are tight with personal information in general and e-mail addresses in particular - they're reluctant to give it up.
You need to "buy" it from them by giving them something they want. And - of course - you want to pay as little as possible!
All of the ideas above are excellent. Here are the things I can think of, some of which overlap with what has already been said:
1. Points/Incentive Program
If you are running a points/incentive program you can explain that a customer has to share their e-mail address to take part. You can even copy the credit card companies (very good at this kind of thing - it never hurts to copy what works!) and offer something like a "new customer sign-up bonus points" - extra points for customers who are joining the program for the first time and sharing all of the information that you want. The thing I like about points is that they are "cheaper" than a straight up discount and tend to keep the customer involved.
2. Fundraising Program
Same as above - if you have a fundraising program and the customer wants to take part explain that your system requires you to enter their e-mail address for record keeping.
3. Reminder Service
If you offer an electronic reminder service to your customers (reminding them about birthdays, anniversaries, etc.) then present it is a valuable service you are offering them free of charge - once that requires you to collect their e-mail address.
4. Electronic Receipt/Invoice
When dealing with phone orders an electronic receipt/invoice sent to the customer can be very appealing. Not just for the records but to catch any mistakes. Tim Huckabee - a sales trainer I really respect - encourages shops to tell the customers to review the receipt/invoice for potential errors (delivery date, address, card message, spelling of names, etc.) very carefully. It's a great idea and you know what? It works - the customers often catch something!
5. Photograph of Product/Delivery
You can also use photographs to get their e-mail address. You might want to e-mail them photos of products they should consider during the sale process or you could promise to e-mail them photographs of the actual finished product and/or delivery.
6. Delivery Confirmation
Explain that if you have their e-mail address you can automatically send a delivery confirmation once the flowers have been delivered.

