At least a silver photo frame if you end up with hundreds you can use for the next christening you go to. Or store them in a drawer to add pictures to as your dc get older.
ds1 received a silver plated faux scroll that you stored your christening certificate in
, all engraved with details of the christening...
So many levels of hideousness you can't begin to imagine but it's sooooo ugly, sooo naff, it's too small for the certificate to go in, got lots of sharp pointy bits that if you did have it out and young child got hold of it they could do themselves all manner of injuries on the wretched thing.
Who on earth wants to keep their christening certificate on display in such a grim thing? Wouldn't you keep it safe with things like birth certificates and passports and suchlike? (or lose it tucked into the family bible...)
And when I came to look at it in detail, they'd got the details on it wrong. Not like I could take it back anyway, but if you were going to get something engraved you would have thought you would have double checked all the details out 
so guess this post is really saying - please do not even consider a fancy christening certificate holder as a present 