I had a Rapha in L; it was still too small for my massive bonce.
I had an Assos Mille and cut the elastic out of the back. That was okay, if a little tight.
I have a Craft summer cap, similarly with elastic removed. That fits me okay, but sadly they don't make them anymore.
I had an orange cap that I got for £3 at the CTC rally, rather like one that Arabella owns. That fitted me fine (you guessed it - with elastic removed) but I lost it.
Finally, I bought a Castelli cap in Belgium this year, it fits me perfectly and I haven't even had to get my scissors out!