The best site I’ve found to view the most comprehensive list of all cruise options is CruiseCompete.
Normally no prices are listed, but you can submit a free (no-obligation) enquiry and several travel agencies will normally respond with their quotations by email within a few days. I recommend you then compare these prices with live quotations from one of the multitude of cruise booking websites. (Just google ‘cruises’.)
Be forewarned that CruiseCompete.com will return many more results that the usual cruise booking sites, so it’s best to make good use of their advanced search features to narrow down the number of results returned.
The last time I booked a cruise online (7 night Western Caribbean with Princess Cruises) I found the lowest price was at CruiseShopping. But it’s definitely best to shop around.
I’ve not booked through the following website before. They claim to accept international customers and I quite like their ’90 Day Ticker’ which shows all cruises they sell which depart in the next 3 months, because cruises are segregated geographically by departure port. Could also be worth a browse: Vacations To Go 90 Day Cruise Ticker.