Silvermoon,
I'd hightly recommend the Palace of Plenty. Varianor was in a much-shortened one-shot version, and I think in general it was received pretty positively. There was a poll over on Paizo of what people's favorite adventure was for that year, and there were lots of votes for that (it was at the top of my list).
Also, 136's "The Coming Storm" would be a great OA adventure. It pretty much was an OA adventure shoved into Greyhawk.
I wouldn't really recommend any of the TSR OA adventures: I find them much too old-school dungeon-crawly. If you don't mind re-writting them, they would provide good inspiration (Especially Ochimo, the Spirit Warrior)
I'm not sure which ruleset you're using, but the reason I ran the Palace of Plenty 1-shot was to test drive the Book of 9 Swords rules for my OA campaign. Many people told me they enjoyed the adventure, but more told me they enjoyed that optional system. My OA campaign is aiming for a Wuxia style (Crouching Tiger, Hidden Dragon, for example), and I was going for a very cartoon anime style (Ninja Scroll was my goal) with the 1-shot, and I'd say it does either of those very well.
~Qualidar~