What is a good Best-man speech?

A good best man speech, should be about the couple from a third party perspective. I'm assuming you're the groom's friend, so give a introduction of yourself (including how long you've known him)...and talk about lame/lonely/losery he was before he met her. Toss a few harmless jokes at the groom. Then talk about the ways he's changed for the better since he met her...and how you've watched them grow together, and want to wish them the best of luck as they begin a new life together. The best advice is keep it short, keep it clean.
I was once at a wedding where the best man told a pair of anecdotes about the groom's masturbatory habits, and the bride's promescuity. Not a good idea.

be gentle, but be funny. cry just a little towards the end. don't make any stabbing remarks at the bride.

If you can pull it off you can always go ultra classy, with a prepared line about what love is from some famous author and if this is really beautiful and applies and is delivered well sometimes I've been surprised at the impact this can make. If it's like a witty Grucho Marx or Woody Allen or something type thing you might get some nice guffaws, but it's hard to go with someone elses jokes. I think that if delivered right and related to the people properly these quotes do work. Personally, my approach would be and has been to talk honestly about your relationship with the person and to tell a story that represents the person to you. Not an anecdote for anecdotes sake- but what story do you have about this guy that represents the kind of person he is. If you tell this correctly, the rest of the audience knowing him, will smile and nod in tacit agreement. Now, is this the wonderful thing that the bride sees in him, and that we all see in him?Or, as someone said earlier, has he changed now because of her place in his life? The bride's relationship to groom in the best man speech I think absolutely must be talked about (the wedding is mostly about the bride in the western tradition) and it works as a good closing to the speech. It may help to think of it as a public opportunity to tell someone how you feel about them or how much they've meant to you, where it's okay and expected, and also if you feel compelled to give details about yourself ( not too much, i wouldn't touch on your romantic life) I think it can make it easier to relate to. This is for the earnest speech, for the wacky speech it has to finely tailored. I'm rambling but I hope some of this could give you an idea where to begin. Good luck.

I was recently at my sisters wedding and the grooms brother was the best man. He was very sweet and caring but at points would through in a funny joke or comment. They dated for 7 years and he said "I can't believe how fast you two have rushed into this!" In my mind you should keep in fairly short, and be very subtle and caring, but lighten in up with a good joke or comment. But keep the comment or joke clean (very good tip!) Good luck and I hope that helps!

I agree. Keep it clean--no embarassing stories!

I agree with what’s been said so far. I work at a country club and I have witnessed my share of best man speeches. I think the best ones are as everyone said: not too long (people have short attention spans, especially after drinking for a few hours) and definitely heart-felt. You don’t have to go on about how you love the couple, but do mention who you are, how long you’ve known the groom, throw in a couple of light-hearted roasts directed at the groom, and if possible, mention how the groom has become a better, happier person because he found the bride. Most toasts I’ve heard follow this sort of formula.

DO NOT: Use foul language, insult the bride, detail anyone’s sexual history. Keep it pretty clean; you want your toast to be touching and moving to all who listen. Everyone wants to laugh a little bit, but mostly they all want to be moved by your friendship to the groom. Adding how the bride has improved the groom’s life is bonus; she will love that and so will all the other ladies in the room. :)

As a best man I assume you know him better than most and you know the changes he has gone through. Write about all the good you’ve seen in him since he has fallen in love. If there are no changes for the better than joke about it but as already mentioned, don’t joke about the bride in a way that would humiliate her or him. They won’t forgive you for ruining their day of joy and you may find yourself no longer his best man.