A lot of the people recommending infodog and such don't do agility afaik...
In many areas of the country, including mine, AKC agility entries cannot be done online. You need to print out a premium (just the entry form page). These are usually found on host club or trial secretary's websites. You can print them out on AKC but usually have to fill in the club information if you do it that way.
I use the AKC event calendar's agility tab to search for trials and get trial dates, opening/closing dates, etc. Then print out the premiums from host website and mail in time for opening day.