As soon as the sun shows its face I get obsessed with Greek salad. I don't know what it is about it, but ever since I got the dressing pretty much nailed last year we have it several times a week; sometimes its a lunch, sometimes just as a side for BBQ or sometimes made meatier with some chicken or lamb for a light dinner.
For me the unarguable components are tomatoes, olives, red onion, good feta and *that* dressing. If I've got romaine lettuce all the better, but to be honest I'm not going to be a purist about it and some crunchy salad leaves will do just fine for me. Cucumber and peppers are optional.
My dressing is half and half red wine vinegar (NEVER white wine vinegar, it just won't work for this) and the best olive oil you can get your hands on. Then, loads and loads of oregano. Fresh is good, dried will do just fine. If you can leave this to marinate with your feta then all the better. That's it. Try it, love it.