How did you score your first corporate gig?

I have a small time word of mouth business (slow) and thought about approaching some of the giants for work. BUT I have no idea where to even start? What type of clients should I bank on? Whats the best method of contacting them? I'm curious to hear of the types of corporate functions you have catered for, were they kids/adults/both? I thought perhaps a letter of introduction, some pictures and info on myself...I never thought it would be so daunting!

I get mine through entertainment booking companies, except Kmart where one of my artists is an employee there as well.

A couple of the ent. companies came to me, while others I sought out and sent them a small promo packet involving an intro letter, a brochure of what I offer and an 8x11 sheet with photos of my work on it.
Then I called them to follow up and it worked beautifully.

Good luck!

Hmm... my big clients found me.

This is not a big city and when I started painting here I was the only professional. I did a couple of corporate christmas parties and then the other large companies started calling to - spouses worked at one company and the whole family would attend the party and the other spouse worked for another company, and they would call and book for their party... and so on.

I also have used targetted postcard mailings to reach out to companies that I haven't been booked by yet.

Most of the large companies actually have employee social clubs that do the hiring for the social events. So address mail to the "Social Club".

The few big gigs I've done have found me.