Their union was overseen by the holiest of holys!! :) The reception was REALLY boring though :) Marriage was created for other purposes further down the road, I don't think that Adam had a tuxedo on, and Eve didn't have a veil to lift.
...Well they did have God there as their witness (and priest... and father of the bride...) and maybe a choir of angels singing 'here comes the bride'... But, had to flub the song about being dressed in white... :-p
The story does not include any details of a ceremony. In the Ancient Near East, marriage was enacted, not simply celebrated. Having sex was the enactment of marriage. Sometimes this would occur prior to the man buying his wife, sometimes it would occur afterwards. In either case, Adam and Eve were recorded as having children, therefore according to the customs of the Ancient Near East, they were married.