I have a website design business with about 100 clients, most of which we host and regularly service. I want to add some marketing services but I want to get some opinions as to what exactly we might want to offer. What kind of marketing services should we offer? I really feel like we are missing the boat on providing marketing services…
Seems like you’re starting from the wrong side… It’s not what you should sell, it’s what you can.
Do you have people with marketing experience on your team? If so, what are they experienced in? And if not, will you be hiring?
This is true Ted, we have experience in many areas, just never packaged anything to offer to our clients. Which is what I believe we need to do now if we want to grow…
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True. In fact, I’d go even further. It’s not so much what you can sell. It’s what the customers want to buy.
Mike[/FONT]
If this forum provides a like button, I will like Ted’s comment 
Bring some social media experts on your company. You can provide social media marketing/online marketing. For e.g. if some of your client need to have an engaged Facebook fan page and thereby get traffic and sale from the page, you can provide it by your service.
Another e.g. you can help your clients in CPC ads like Google Adwords. It is really tough to spend money on adwords and make sale. If you have some expert on your team, you can provide the services.
So that’s where I’d say you start 
If you want to list out the areas of expertise and degrees per each I’m sure we can provide more thoughts on what’s hot.
Those questions are definitely worth to decide about the services of marketing?
And these questions can also be considered… What kind of case studies ,you have done? What’s Your specialty? Etc.