it is my sisters special day and she means the world to me
That's a great place to start!

Your speech doesn't have to be long, a few words go a long way.

I did a speech at a friends wedding. I talked about how we met, how long we've been friends, about how she met her husband then i wished them well etc. I ended with a quote I found which got everyone laughing and left them them a squishy lovey 'awww' type feeling.

Here's what i said (word for word), feel free to use it if you feel it fits in with what you're going to say.

I'm going to end with a quote (from a very wise woman ) - Oprah Winfrey!

'May your marriage never know conflict or competition'