I'm a bit hesitant to mention it as the price might go up to match other Greek EVOOs, but Tera Creta is very good. I don't belong to Costco (two person household), but one of my neighbors does, and I've sampled some of the organic 'Kirkland' EVOO she gets there. It's a good example of a late-pick ('buttery') EVOO (and a lot cheaper than what I've been paying for EVOO).
If price were no object I and wanted Greek, I'd probably get 'Mr Papous', but I prefer to visit relatives in CA, go to groves in the Sonoma area, support those farmers. There's also really good EVOO coming out of NZ, but I've never managed to visit a grove during one of my visits.
As an aside, then only way to get into a Costco without membership as to tell the door person you're there to buy a gift certificate - and there's nothing to keep you from using that certificate right then... :-)