My clients are pretty large, well most of them, in fact I intend to put a PR in the PR section this afternoon regarding another big name you will be aware of.
In my opinion never leave VM its a waste of time, if you do mail follow up within the week whilst its still in their mind. But there is nothing better than speaking to the decision makers directly, some people hate doing it but it works ask if there is anyone else they know who may be interested, mention some of the great work you have done in the past, once you have one big name on board you will be amazed to see how easy it becomes to get others.
OH and the script you use is key, keep it short and sweet and to the point, qualify there interest, if you have a newsletter ask if they mind if you add them. I only have 150 people on my mailing list but I would say 100 of them are within multinational companies that turnover Millions or in some cases Billions.
Let me know if I can help anymore.
Michael