If you want the taste of olive oil to star, use a good quality, otherwise a vegetable oil is fine.

Tarragon
Whisk 1/3 cup oil with 1 tbsp. tarragon vinegar, 1/4 tsp. Dijon mustard and a pinch of salt.  Great over asparagus. 
Makes 1/2 cup.

Curried
Whisk 1/3 cup oil with 1 tbsp. lemon juice, 1 egg yolk, 1/4 tsp. curry powder and a pinch each of sugar and salt.  Excellent over greens with hard cooked eggs, chicken or seafood dishes. 
Makes 1/2 cup.

Greek
Whisk 1/4 cup olive oil with 2 tbsp. red wine vinegar and a pinch each of dried leaf oregano and slat.  Add crushed garlic and mashed feta cheese.
Makes 1/3 cup.

Italian
Whisk 1/3 cup olive oil with 2 tbsp. red wine vinegar, 2 tbsp. freshly grated Parmesan cheese, 1 clove crashed garlic and a pinch  each of granulated sugar, dried leaf oregano and salt. 
Makes 2/3 cups.

Fruit
Whisk 3 tbsp. oil with 1 tbsp. lime juice, 1 1/2 tsp. liquid honey and a pinch of salt.  Add 1 tsp. poppy seeds.  Pour over fresh fruit on a bed of crisp lettuce. 
Makes 1/3 cup.

Dijon
Whisk 1/3 cup oil with 1 tbsp vinegar, 1 1/2 tsp. Dijon mustard and a pinch of salt.  Drizzle over smoked salmon, cold roast beef or chef's salad.
Makes 1/2 cup.

Mexican
Whisk 1/3 cup oil with 1 tbsp. lemon juice, 1/4 tsp. ground cumin and big pinches each of chili powder and garlic salt,.  Great with avocado, tuna, chick peas or tomatoes. 
Makes 1/2 cup.