Vinaigrette can be as simple as 1 tablespoon vinegar to 3 or 4 tablespoons olive oil, plus salt and pepper. Classic French versions add Dijon mustard and herbs. Lately, I've liked using sherry vinegar and rice wine vinegar in equal parts, and peanut oil and olive oil in equal parts, with a little lemon juice:
1/4 cup Sherry vinegar
1/4 cup rice wine vinegar
3/4 cup peanut oil
3/4 cup olive oil
Juice of half a lemon
Salt and fresh ground pepper
I buy a terrific brand of rice wine vinegar from Pearl River Bridge (their Soy Sauces are also very good). Terrific value and available at almost any Asian market.
Sherry vinegar is a little trickier to source. I've never seen a decent anywhere but specialty markets. Here are a couple I've used with success brand from Paez Morilla, Jose Paez Lobato and L'Estournell. I avoid Don Bruno (actually from mass producer Roland), and Columela, though these might be found in mainstream groceries. Search Amazon.com for sherry vinegar.
vOne I don't think I'll try is La Bodega, individually numbered, only 4,000 bottle made per year, at $45 for 6.8 ounces at Williams Sonoma.