The best weddings I have ever been to (my own included) were where the guests all pitched in with the jobs. I had my SIL and an ex boyfriend take the wedding photos. It worked fantastically as she is a press photographer, so got the action shots, and he is very good at portraiture and took some stunning shots of the guests (my mum has even nabbed one he took of my dad 'for his funeral')
I catered my eldest sister's wedding myself, with help from a friend. I also drove the wedding cars which we decorated with ribbon matching the (homemade) bridemaid's dress. My brother's were the barmen.
For my wedding the son of a friend who is studying music technology was the DJ, though we made sure we burned 2 CD's of our favourite music. Actually, those CD's were the best thing. When we want a romantic evening in we open a bottle of Red wine and play them. We walked back down the isle afterwards to Primal Scream announcing 'You know what we want to do? We want to have a party!' Which raised a huge laugh.
I also did the Marks and Sparks wedding cake bit, decorated with red and white carnations bought at 2 quid a bunch from the corner shop. I made the buttonholes from the same flowers, just get yourself some florist's tape, wind it round the stems and add a safety pin.
I had no flowers, didn't want them. At the last minute the best man's wife gave me a 'goth bouquet' of dried flowers and feathers, which still has pride of place in a vase.
We made the invites at home on the PC using Microsoft Publisher and a scanned image of ourselves looking drunk and silly on the front. We printed these off on nice linen paper bought on a BOGOF at WH Smiths.
Lasvegas, I don't think vouchers are at all a bad idea. We asked for them because we were both in our 30's and had everything we needed. But I was 7 months pregnant so we wanted a new washer/dryer. It meant that even the poorest friends could contribute a fiver and know they were getting us something we really wanted.