I checked out your Website, you've got some good workshops coming up. I think the type of workshops depends on your clients and where they're at in their business - for example, I find start-up business owners are often interested in information on finding funding, business structure, and marketing.
Have you tried polling your clients - and asking them what workshops they're most interested in? There are several free online polling software that you can use to set up a poll - such as "Survey Monkey" and Wordpress offers a plugin as well. Or of course, you could send one by snail mail to past and current clients.
I agree with Rae that social media is a hot topic right now.
Hopefully more of the members here will see your question and take the time to answer too...
Good luck with the workshops, they're a fabulous idea for business owners.