take a look at interlinetravel.com, too
user interline, password nonrev
no fee outside 3 days for payment

I'd take a look at all the sites and call once for advice about timing. You cna sign up for all of their specials and get email flashes with deals every few days. dargal is canadian, perx and interline are texas, if time zone is an issue for contact

interlineone.com is a new one I've just seen recently wiht good booking engine but no experience with agents

I personally would not book anything too far in advance unless you have a certain cabin request. so many of these ships have balconies now. I just booked a short family cruise for 10 days off--many of the well-priced cabins were gone, but I had a bunch of gift certificates to use up. personal recommendations would depend on your age group--particularly Alaska. I think rankings are:
carnival
ncl
rccl
hal/princess
way up from there--azamara, seaborne, luxury lines, etc
However--each line has premium ships that may beat the pants off another line of a higher ranking.
I haven't broken down to want to cruise Alaska yet--just a warm-weather-ship-kinda-chick. But I have gold status on NCL from more than 12 cruises.
hope that helps not hinders

oh meshpo--take look at cruisecritic.com for advice from pax--go to forums by cruise line