I was in the same situation about 10 years ago (yeah, pre-1.0-burst) so I think I have some insight for you...
First, this is a business question you are asking in a techie forum, bad idea. You are running a business, possibly selling a business, go get yourself some business advisers, at a minimum that means an accountant and a lawyer who know (or at least "get") your industry, and preferably some people who have sold companies in your industry, extra points if they sold to the same megacorp and aren't involved with megacorp any more (they can tell you how it all went, but if they're still there, there's a conflict).
Second, and read carefully: TAKE THE MONEY. There's an old expression: No one ever went broke making a profit.
Caveat: after taxes it should be more money than you'd make in 10 years of working the same "job" at average pay. (e.g. if you're an engineer who could easily pull in $125k/yr, make sure you're landing at least $1.25mm cash after taxes, don't take an all-stock deal - bubbles burst) You need enough money to be able to screw around for a few years if megacorp really does turn you lazy.
BUT don't get sucked into a long term contract working for megacorp. A year or two is ok, and if you're stuck with an earnout, make sure you really can see your company meeting those numbers. After a year you could be itching to leave the megacorp lifestyle (no company is perfect) and its best to know you can part on good terms, pick up and travel for a few months, then start your next awesome company.
Third, can I repeat #1? Find a better place than slashdot to get this sort of advice. If you're really strapped, try your college's career center network, or SCORE (.org)