Pop Quiz = Not looking at the other posts before responding, so…
Find a safe place, preferably home. Call the business card. Ask if he lost his wallet. Ask to describe the contents. Agree to meet with him for delivery or mail it to him (if he doesn’t mind the wait and/or is inconvenient to physically get to).
Simple as that.
Now, upon reflection, I may want to contact the police, for fear of being accused as a thief.
That’s all.
I’d return it, with the money. I’d be no poorer than I was before I found the wallet, and I’d have the happiness of having done someone else a big favor. I’d absolutely refuse a reward, too.
I think a big part of this is that I am financially secure right now. A few years ago, when I was a student struggling to make ends meet, I might have kept the money. Then again, maybe not – I found several purses in different campus libraries and always returned them. It’s hard to say.
eunoia, that’s the best answer yet. You are very evil.
As for myself, I’d return everything intact and expect nothing in return. $500 comes and goes, I’d rather make someone’s day.
Brown paper bag/unmarked briefcase/black duffel bag of money with no identifying marks - well, that’s mine no question - be it $20 or $20k. Who carries cash around like that anyway? I’d just hope it wasn’t marked or anything - wouldn’t want to get caught up in some drug cartel/mafia mess.
I wouldn’t assume that it is a terrorist booby-trap, because when we start thinking that wallets on the sidewalk are terrorist booby-traps the terrorists have won!
I’ve found cash-/credit card-filled wallets before and returned them. I’m not sure it means I’m a really honest person. It’s more that I really like the good feeling I get seeing how happy people are to have their stuff returned.
I’ve been on the other side too. Years ago, when I was young and stupid, A packet containing my travelers checks, money, credit cards, and my passport fell out of my bag at Heathrow airport in London. (Yes, I was very, very stupid to have that all in one such vulnerable place. And yes, they did have planes back then.) Someone returned it. I didn’t even know I’d dropped it till I heard a mangled version of my name being paged. I would have been SOL if the finder had been dishonest.
Call the guy, find out, and return it.
I had a lovely incident a few months ago - noticed a bag in my coffee shop, filled with stuff. I turned it in, didn’t think about it. The barista saw me a week or two later and presented me with a small bottle of very fine Benedictine, a gift from the owner who thought she’d lost her wallet, ID, cell phone, etc.
BTW, you never know why someone’s carrying cash. You never know if someone’s just graduated from law school, carrying $100 grand of debt, and is paying their roommate their share of the rent.
As most everyone else has said, return it intact. About this time last year, I managed to drop my wallet on the way to a baseball game in Tampa. Didn’t notice until I got there and couldn’t buy tickets. And when I got back home, some one had dropped my wallet on my front door (which is fine; I’d dropped it in the parking lot, after all), sans cash.
For some reason, that irritated me a bit. I mean, had the person returned it and left contact information, I would have GIVEN him or her the cash, but while returning the wallet and not using the cards or anything is certainly admirable, taking the cash is, to me theft. And I’m sorry, but that’s just wrong. As Shodan said, my integrity is worth more than that.
Returning the wallet with everything intact would give me a lot of pleasure. For me it’s just the decent thing to do.
Twice in the last two years I’ve lost my wallet – once at an airport. It was turned in to Lost and Found with everything in it. The second time was after my wallet was stolen in an armed robbery. Someone found where it had been tossed out and called me. When I went to pick it up, it was in a fairly poor neighborhood. Yet the woman refused a reward. But she had a cute little girl sitting on the front porch and I suggestee that she might take her granddaughter to lunch. That made it easier for her to accept and it made a little girl smile. It made me feel better after a rather traumtic event.
They caught the man who stole it after a long chase through half of the county. He’s doing time. The poor thing made the mistake of robbing two teachers. You’re not going to get any money that way.
I did make him give me my purse back though. 
I’d return the wallet as is to it’s rightful owner. I wouldn’t even be tempted to take the cash (and god knows I could use it). That’s out and out theft in my eyes.
Now I have found money on the street (most I ever found was $80) with no wallet and no one around that could have dropped it and I’ve kept it. If the amount was over $100 (well, $200) then I’d turn it in. I can’t see how the police could track down the owner of money with no ID what so ever but I’d at least feel better that I turned in a chunk of money that large.
I’d return it intact, just because that’s the right thing to do. I figure if something doesn’t belong to me, it’s stealing to keep it, especially if I can find the owner.
My daughter found a scooter at the park last summer. She desperately wanted a scooter at the time, and it was past her birthday and a very long time till Christmas, but she took it around the neighborhood asking kids if they’d lost it. Then she came home and made up posters which she tacked up at the park. After two weeks of getting no response, she and I finally agreed she could keep it, but I know that if the owner turned up now, she’d give it back gladly. I’m proud of her for that.
If I found a bag of cash with no ID in it, I’d turn it into the police (and get a receipt), but more because I’d assume it was the proceeds of a crime than because I was concerned about the owner.
Hmmm… A moral conundrum. Well, I guess I’d probably select one personal item from the wallet, such as a family photo and cut off an identifiable piece of it and then mail that piece to him/her together with a note reading “we have your wallet. If you ever want to see it again leave $2000 in subway station […] locker no. […], then take the key to […] park and leave it at the foot of the […] tree. If you contact the police, the wallet gets a one way ticket to the garden shredder.”
Upon reflection, that smells like a lot of work… heck, maybe I’d just give it back.
If you’d have asked me this question a few years ago, I’d definitely have taken the cash. Now, because I’ve benefitted from the kindness of strangers on a few occasions since, need the money a little less but mostly because I suffer from a more highly developed sense of morality, I wouldn’t hesitate to give it back.
Who says you lose out by being ethical? 
I’m sure I would return it. I seem to have the reverse of the problem many people seem to have with hypothetical moral dilemmas: once I’m in the situation, I always do the right thing without thinking about it. I could sit here pondering, “Yes, but what if … maybe I really need the money … maybe I have reason to think the owner’s a jerk …” But when something actually happens, none of that occurs to me. Go figure.
Closest I’ve come to a windfall of this type was when I pulled up to a drive-through ATM machine to find that the previous user had left his card in the machine. Not just sticking out-it was all the way inserted, and the display was blinking the message, “Would you like another transaction?” I hit ‘no’ immediately, of course, rather than cleaning out his accounts. Eh, probably would have gotten caught anyway-those ATM’s all have cameras …
Hmm, tough call. $500 US is about $800 CAN. I’d hate to say it but it might depend on how I got the wallet. If it was in a public place and an officer was near by (or the station), I’d hand it to him, intact. If I had to spend too much time with it (say, in my car) I might honestly take the money but leave the CCs alone and drop it off at some mail box.
When I lost my wallet I got a call that day by VISA regarding some unusual charges on my card (by, ironically, the downstairs clothing store in the building I worked for). I didn’t pay anything to get those charges returned and new cards sent to me.
I have returned a cell phone though. I determined it wasn’t one my company offered so I checked the company it belonged to and returned it to the nearest store. Maybe because I work for a cell phone company that my priorities are screwed.