First thing's first, do not buy taxable bonds with that much money, that'd be idiotic. That's what munis are for. You're welcome, I just saved you hundreds of thousands of tax dollars.
Next, do some thinking. What's important to you? $25mm is enough to retire on, but not enough to live like a celebrity on, so be careful. Are there any nonprofits you care about? Is there some career you've always wanted to do but it didn't give you the income you needed? I'm thinking things like ski instructor, golf instructor, charter boat captain, things like that. You now have the resources to do those things. or, do you simply want to continue working and allow the money to grow?
Once you've decided your general direction, hire an attorney, estate planning mainly. You want to have this money put into various trusts so that you can access it during your lifetime but also so there are some tax savings and creditor protections put in place. Also, you should be able to divorce proof some of the assets if you put them in irrevocable trusts before you're married. Sidebar: get a prenup signed.
Next, you'll need to manage the money, so I'd interview at least 3 financial advisory teams. Sure, you could manage it yourself, but there are 3 big risks to you losing all of this money: predators, your emotions, and overspending. A good FA will help you avoid all 3 of those and while you'll pay a fee for it, a good advisor at this level of assets is worth his weight in gold. If you need help choosing, feel free to ask.
People will come out of the woodwork asking for help, tuition for some summer class, help with medical expenses, help with debt, new clothes, and more. Just say no. If you have a problem saying no, tell them "let me ask my broker," that will usually shut them up because your broker won't advise that you give away all your money. What I'm not saying is don't help ANYone. If I had that much money, I'd definitely clean up all my parents' debt and any medical expenses they needed, but where you get into trouble is by improving the lifestyles of other people.
It's my guess you're under 30 and have limited experience investing (you mentioned your associate, so that tells me you're an analyst, likely in banking). Your emotions are the devil. At your level of assets, most advisors will recommend something called a "core-satellite" model, which basically has a balanced stock/bond allocation at its core (say 50/50, 60/40, etc.) for the bulk of your assets (say 15mm), and 10mm of satellite strategies, maybe 1mm in a trading account that you control, 2mm cash, 5mm in PE (good advisors will have access to PE deals you can't participate in off the street), and so forth. Sure, you could put the whole amount in vanguard, interactive brokers, eTrade, but how much time do you want to spend on your investments? If you want to do that, knock yourself out. I think it's a stupid idea, and I invest other people's money for a living. If I came into that much money, I'd hire a team to manage it for me, and then I'd go to the beach. Having someone to run your decisions by on a regular basis is important, especially since they'll have more experience than you.
Don't buy a $5mm house, don't start buying ferraris, don't buy a private jet. Assuming you're only spending the interest from your assets, at 2% div yield/muni coupon, that's only 500k/year after tax or a little over 40k/month. Your goal should be to not draw down the principal of this money. On 40k a month you can live a wonderful lifestyle, but you cannot own 3 properties in big cities, eat filet on a regular basis, charter jets to exotic locations for all of your friends, and so on, without overextending yourself.
If it were me, I'd get all the legal/advisory/tax stuff taken care of, and take a year off. Maybe rent a nice place for a year (not just one place, maybe a loft in NYC for 3 months, beachside house in australia for 3 months, backpack europe, and then island hop for another few months in the south pacific) to see how you like it, travel, volunteer, and so on. When you get back to reality, you'll know if you can do that on a constant basis. At this level of assets, you could really just dick around for the rest of your life, but my guess is you'll want something else out of life. It's my guess that "something" isn't investment banking or business school.
Feel free to ask more questions either here or via PM, I have to answer this question from time to time if a wealthy client dies and the kid is wondering what to do.
Mod Note (Andy): This comment from 7/20/16 was originally posted in the thread Just won lottery ticket and received 12 silver bananas so we thought it deserved its own spot on the frontpage