Axe - aside from Gringo's pomposity, perched upon his bar stool, you might consider:
1, Xunatunich in Cayo. Easy to get to, near the Guat border, west of San Ignacio. Lots of places to stay, in wide variety of pricing. Funky little place I like is Parrot's Nest in Bullet Tree Falls, on the Mopan. Pretty basic so that impressing the Ozzie might rule this one out. http://www.parrot-nest.com/
Check out http://www.evasonline.com/pages/page2.htm
for some other ideas. You can also hit ATM cave in same area and do some cool canoing as well as other things. Another place I like is Clarissa Falls. Both of these do not cater to the high-end crowd but are charming & funky in their own right. Neither get much, if any, press from ppl on this board, but that's ok too. Simply means it's a little less crowded.
2. Lamanai is a also a very good ruin site, easily done on a day trip from AC. Better than Altun Ha, in my opinion. Acco's are relatively limited. Lamanai Outpost Lodge is nearby. Maruba not THAT far away, if you want to pamper her a bit.
No doubt others will chime in here as well, but this should get you started. Just be sure to schedule around the cruise day-trippers.