I saw gogamer has ArmA's Queens Gambit
for $6 for its 48 hr madness (though its showing as 109hrs left as I post). Beats paying $20-30 for it as I've heard that while its better missions than ArmA's OC its short. While I want to play its missions, I'm mainly getting it for the new island and units since a lots of mods are starting to require it. Low price finally puts it in buy mode as I wasn't $20 missing the new content.
I also noticed that Amazon has vanilla ArmA for $15.
(Gogamer still charging $40 for it). Not bad to get basically the gold version for $20 when the actual gold package is $50.
Be sure and nab the latest patch (beta 1.12) as it definately improves a lot the release bugs/ai issues. Grab some good mods based on this realism and immersion guide
. Additional big gameplay/AI mods to check out are SLX
Of course if you didn't like OFP you won't like ArmA as its basically OFP with a facelift (think OFP 1.5) and many feel that OFP + graphic mods are just as good. I like and still play both though mainly for custom missions and the editor.