The www.ticketclic.it website mentioned in the Rome guidebook is no longer handling online sales for the two-day combo-ticket. I have received an email from Omniticket informing me of this. The new official website is operated by CoopCulture. Their direct URL is: http://www.coopculture.it/en/colosseo-e-shop.cfm To make sure that this is accurate, I have contacted the hotel where we are staying in Rome next week, and they have checked and confirmed this for us. The prices remain the same as before, and we have purchased our tickets online with no difficulty earlier today. You can print the tickets off in advance to avoid the long lines that Rick has warned us all about. My wife and I are staying at the Palazzo Cardinal Cessi (1 block away from St Peter's Square) for four nights, and will report back with our impressions. Hope this update is helpful to most everyone.
All the best.
Brett.