Forbes contributor Ken Kamen has a great piece of advice:
Don't do anything right away. Take some time to catch your breath. Being in the middle of a whirlwind of change is not the time to make any big financial decisions. Park the money in the bank for a while, and don't rush to write any checks.
From the WSJ:
Before making any important investment decisions or purchases, sock away your wealth in a safe place, such as a money-market account or short-term certificates of deposit, advisers say. Set aside a reserve fund that you won't touch. The fund should cover at least 18 months of expenses.
At some point you'll need a "gatekeeper," whether it's a an accountant, attorney or financial adviser. Here, you have to be especially deliberate: When word of your winning starts to spread, you will be inundated with offers from all kinds of money people with all kinds of charts and graphs that are supposed to prove how good they are at handling other people's money. Their talent - and motivations - are likely to run the gamut, which is why you need to be super-selective. You will learn that the managing your fortune is a job in itself.