I used ebonyink -
www.ebonyink.com.au; they were happy to design exactly what I wanted, and it wasn't expensive at all...
They have this one:
Ebony Ink - Gerbera Wedding Invitation and Wedding Stationery
They will change the colours to whatever you like, but if you prefer something else, just email them with your ideas and they will email back and forth with you until you design something you want.
They didn't charge me any extra to have my invites custom designed, so we explained what was in my head and that's what they did :)