A bit old now, but I had a naming day for my DD last year.
WE did it as a big party and then the ceremony was done like a big 'speech'. We had a guy from the Humanist society who came and led the formal bit. He spoke about our hopes and aspirations for our DD, how much she was loved and wanted, etc etc. We had a couple of poems read and her 'guide parents' (and us) made promises to be there for her etc etc.
Then we gave her a gold bracelet and the officiant gave a toast to our DD. Everyone said Cheers to her and we all ate food and had a party in the afternoon. It was a lovely day, and I've had loads of comments about how great it was. The only thing I'd change was next time I'd do it in a hall. (We did it in our back garden) I don't think it would be that much more expesive as then the guests would buy their alcohol and that would probably pay for the hall hire!
The humanist society do actually do a booklet that has ceremonies that you can just copy, or lists of readings etc to choose from if you want to make up your own. Its well worth buying.
Oh, the other thing we did was to make a book of wishes that we got people to write in for our DD. On one side of the page we put their photo, and on the other we got everyone to write her a message... She has some gorgeous meesages, some are really from the heart, and all the family ones are about how much she is loved, how wanted she is, what joy she brings to the family etc etc as well as people wishing her the best for her future.
HTH