If you are close to 3-months since the stent went in, it should be well overgrown with new arterial epithelial cellls by now. So the risk of restenosis from stent-induced clotting is pretty small.
When I had my stent put in, I only went on Plavix for 90 days, along with a daily 81mg enteric coated aspirin and warfarin (which I'd been on for awhile anyway, due to a previous pulmonary embolism). I still take the aspirin and warfarin, but if it weren't for the PE, I'd be on only the aspirin for life.
For long term therapy there was a recent study (New Negland Journal Of Medicine) that found that aspirin by itself was just as effective as aspirin plus plavix, and better then plavix alone (as aspirin has a lower risk of bleeding episodes), at preventing recurring MI's in people who already have heart disease (and at a fraction of the cost too).
edit: the study was "Clopidogrel for High Atherothrombotic Risk and Ischaemic Stabilization, Management, and Avoidance (CHARISMA)"