I am the groom on this occaision. What on earth do I say, bar the thanks for coming and toast my lovely wife you drunken sots?
Would I be correct in presuming that putting a bucket in the back of the room and telling that they can make their cheques payable to me would be considered bad form(I'm bloody paying for it)?
Yeah, I think that would be a bad idea. Pissed off, cheap and smart-assed are probably NOT what you want to convey.
My main advice would be to keep it simple, and don't try to come up with some wonderful stuff that is totally out of character for you. Your advantage is that everyone wants to get on with the party, so nobody will get mad if you don't talk long enough. Weddings are mainly for the bride anyway (as far as the "big event" aspect of it goes), you are probably just going to be acting as a prop on the wedding day anyway.
Well, if you have any naval guests, bear in mind that there's a time-honored tradition of sending telegrams to the groom containing scatological jokes dressed up in navalese. One of my favorites:
Your attention is drawn to Book Of Regulations BR(416), "Precautions Before Opening Unventilated Compartments".