Sorry about the late answers! Different time zone from you guys . . .
Some of these have already been answered in the posts above. Some really good guesses that would actually be feasible answers, but not the one I was looking for. Here's the answers to some of them:
1) Why are manholes round? (several reasons possible, but one really good reason)
Glavinsolo got this one: "f they were square then they would fall right through and hit the person below. Made them round so there would be no way for them to fall through, it won't fall through by placing it at a diaganol, it is the same throughout the circle."
2) What's next in the pattern: 1, 11, 21, 1211, 111221, 312211, . . .
I think Glavinsolo also got this one, but you put a 2 instead of 1 for the fourth digit. Should be 13112211. Read out each preceeding number out loud. Count how many digits there are of each distinct number. For example, we start with
1 (how many ones are there? There's one 1, or 1 1, thus the next line)
11 (how many ones are tehre? THere's two 1's, or 2 1, thus the next line)
21 (now there one 2, and one 1 (or 1 2 and 1 1)
1211 (now there's one 1, one 2, and two 1's, or 1 1, 1 2 and 2 1's)
111221 (repeat).
3) You are caught by natives on a remote island. They have sentenced you to death. They tell you, you can make any one statement. If the statement is true, we will drown you, if the statement is false, we will burn you. And no, your statement cannot be an opinion. What one statement do you make to escape?
LeiZaK got this one: "You will burn me to death." It's an impossibility for this to be true or false given the conditions.
4) Out on a desert, there is a trail of clothes, followed by a short stick, followed by a dead body. Why/How did he die?
HonkeyDonk got the textbook answer for this one. This one's hard to figure out w/o a series of yes/no questions first.
5) There are 53 bicycles found on green carpet. A man is dead on the carpet w/ a gunshot through him. Why/How did he die?
Glavinsolo & Leizak got this one (Glavinsolo got the main idea, Leizak refined it). They are playing cards and he cheated by brining an extra card.
6) A man walks toward home. He notices two men in masks at his destination. Once he gets there, he eventually goes off running making three left turns. What's going on?
Leizak got this one, it's baseball. This is the first riddle of these sorts I ever heard in my life. Loved solving riddles ever since.
7) Gargomoyle (sp?) has captured 50 smurfs. He tells them, "Tomorrow is your execution day. But I will give you a chance to live. I will line you up, all facing the same direction. I will randomly put either a black or white hat on your head. Starting from the smurf in the back (the one who can see the other 49 in front), if you guess the correct color of your hat, I will let you go." The smurfs have one night to figure out a plan. What plan do they come up to save the most # of smurfs? (Note: a smurf can see all the other smurfs in front of him. The 50 hats are randomly distributed (can be 25 white - 25 black or 3 white - 47 black).
I refuse to answer this one. (= this one's a favorite riddle of mine. Took me one looong car ride to figure this one out. You guys figure it out for yourselves!
8) A husband and wife are stopped at a gas station to fill up their car. The husband gets out to pay the cashier and use the toilet. When he gets back, he finds his wife dead and another person in the car. The doors were locked since he left for the gas station and not a single window is broken. How did the third person get in the car?
JToxic got this one. "His wife had a baby and died during childbirth"
9) A man driving a car runs out of gas in a residential neighborhood. He goes to the first house he sees and rings on the doorbell. Nobody answers. He tries opening the door and finds it unlocked. He walks inside the house and opens another door. He sees something and realizes his life is in immediate danger. What did he see?
This one's pretty tough w/o answering some yes/no questions first. He saw a KKK suit in a closet, and he's a black man. Yea- I don't particularly like this riddle either.
10) A frat is holding a party. One student leaves early. Later, it's discovered that everybody at the frat party died from a fatal poison found in the punch. The student who left early was one of the first people to drink from the punch, but he suffered no ill effects. Why not?
Good guesses here. The poison was actually in the ice. The poison hadn't melted by the beginning of the party, thus he was unaffected.
Alright guys: someone figure out #7!