Let's face it. Being able to give a good toast is an art form (in my opinion). I have personally and professionally seen many a toast drag on for 15 minutes only because the toaster couldn't appropriately articulate themselves, or simply wasn't very prepared. Don't let me sound like a negative nelly about toasts....when they are good, they are GOOD! I love it when it includes just enough sentiment and humor, the key is to not embarrass or divulge anything too private. I have created a method to giving a well rounded toast...this is certainly not the only way to do it, but I find that it gives a good outline.
Open with a nice story about which member of the couple you're closest to (how you know them, how they've affected your life, something along those lines). Offer an insight to their personality, this is a good time to include a funny story. From there you want to bring in their new husband and wife. Things that you really like about that person...and the kicker is how they make one another better. Close with a humorous story about the two of them and your wishes for their future. Raise your glass!
Pretty basic outline...don't be afraid to change it up a bit, thats just a safe route to go. Also, try to limit your wedding toasts to about 2 people (Maid of Honor & Best Man). If you're lucky enough to have multiple people who want to toast I would suggest spacing them out during the rehearsal dinner.