I am a West African student, who attended a credible UK institution and graduated with a 2:1 (Business Information Systems. Not really sure what that equates to in GPA terms). I have 3 years work experience ( 2 as a Business Analyst and 1 year in Business Development for a leading Global Business and Technology outsourcing firm). I'm 26 years of age.
I would imagine the West African element adds a little to the application, so thats a plus. The 2:1 is hard for me to understand (I stopped British school after a-levels), so I can't comment there. 3 years work experience is solid, though 2 years as an analyst and 1 in business dev doesn't sound particularly spectacular. This is the hardest part to judge -- were you promoted quickly? Have lots of responsibility? etc.
I am a co founder of two online ventures, with a healthy list of volunteer/community activities and extra curricular activities.
Successful online ventures? If so, I'd say thats quite noteworthy.
I scored a 660 on my GMAT. What do you think my chances are of getting into a top US MBA program (e.g. Sloan, HBS, Wharton, Columbia etc)
I think the 660 hurts your odds at these tops schools to some extent, but admittedly, 700 is just an average - someone has to score less.
I see nothing that immediately tells me you could not be admitted to these schools, but I also don't see anything that leads me to believe you would. Thats not to say you have no chances -- you may well have, but unless there is something 'behind' your description of yourself that makes you unique (the online ventures may be it), your overall background strikes me as mostly 'average'.
Dont' despair. It's partly about how you position yourself. I myself asked the same question two years ago or so and got back something like "You should go to Georgetown"... A few months later I asked again -- having "rebranded" myself and my experiences and got a "you seem like a fit for HBS". The gap wasn't that I'd actually changed my background, unfortunately time travel wasn't invented yet, but that I'd simply learned how to position my stories a bit differently.
I'd encourage you to consider the same -- how do you differentiate? How can you make a year in as a business development analyst at a tech firm sound interesting to an adcom? What makes you different from the person applying from Australia who works in IT or the person from Tata or even the banker from NY? How can you position your stories so that they sound genuine, interesting and unique?
If the question stumps you completely, thats OK. Its not an easy one to answer. What you really need to do is think about your past 3 years, what matters most to you and why, what fits well with your intend goals, what stories highlight something notable, and how do they all fit together to paint a picture that says "African student with amazing experiences and broad multi-cultural civic interests wants to come to our school" instead of "Analyst with 3 years of experience and some online WoW level-60 character wants to come here". I'm exaggerating on purpose of course, but the idea is basically that - think about what stories make people raise their eyebrows (in a good way) about you, or which would make your peers impressed or those that you most enjoy telling (usually the most interesting).
Certainly consider retaking the GMAT. If you are serious about these top schools, a 700 plus, particularly if you think your undergraduate academics are less than ideal (are they? I have no idea), would serve you well.
Hope that helps. In short, I think you have a profile that could be successful, provided you put in the necessary effort and time. I'll warn you now -- "necessary effort and time" is a lot of time and a lot of effort. Not just for you, but for anyone serious about a top university. Be prepared to work for it.