Hello from Abu Dhabi!
I learned somewhere that the basis of a simple viniagrette is oil + an acid + seasoning, which helped me a lot in making new combinations (and also in replicating things I have liked in restaurants). For the acid you can use citrus juices like lemon or orange, freshly squeezed if possible, as well as different flavored vinegars. You can use the ratios in Gracie's recipe above as your guide -- usually about 1 part vinegar to 2 parts oil, more like 1:1 if it's citrus juice. I live alone so I make my dressings in smaller amounts, sometimes just for that day with a teaspoon of oil.
For the seasoning you can add dried or fresh herbs, mustard, or for a change you can use a sweet element like maple syrup, honey or sugar, or a fruit juice. A sweet and sour dressing is especially nice in a salad that has greens mixed with fruit like pomegranate seeds, sliced mango or orange, or raisins or dried cranberries. Dried cranberries are hard to find here, so everyone that comes to visit me is required to bring a large Costco-sized bag of them in their luggage! Sometimes they show up in the baking section, though.
Do you have access to a big international supermarket like a Carrefour or Lulu? Check the Asian or "ethnic" sections as well as the regular vinegar section for interesting oils like sesame or peanut, or rice vinegar, which you can use for a Asian-style dressing (along with a little soy sauce). At first when I got here I tried the regular sesame oil in the cooking oils section and it didn't actually have any sesame flavor. Rice vinegar is a little milder than regular vinegar and I actually tend to prefer it for most of my dressings.
For sturdy greens like spinach salad I add a little balsamic vinegar to the regular vinegar. The New York Times food section the first week of January had a spinach salad topped with green beans, potatoes and feta, and I made it for my mom in the U.S. when I was home. The dressing was a viniagrette with the addition of mustard and yogurt that was very nice.
The biggest problem here is actually getting lettuce-type salad greens. Because it's so hot, almost all of them are flown in from Holland and tend to be pricey. I have been using a lot of cabbage and romaine lettuce, which comes from the Mediterranean and tends to be more available, and growing spinach in a box on the balcony.
What kinds of salads are you making?