Rice vinegar is made from fermented rice. So, if you are avoiding grains you will be avoiding rice vinegar. Now some people can handle a little bit here and there but others want to avoid it 100%, If you are like me, I prefer to buy as few groceries as possible and get the most use out of each one. For that reason I like to find the most versatile food products that I can use in the most dishes. Vinegar is one of those and my number one choice I find can replace most all other vinegars is Raw Unfiltered Apple Cider Vinegar and so, for the most part, that is the only one I keep on hand. Any recipe that calls for vinegar of any kind I use Apple Cider Vinegar. There are only a few very specific recipes that may call for a very specific taste, say, maybe it needs a balsamic vinegar or something like that. Here are some great alternatives to Rice Vinegar:
Apple Cider Vinegar
Champagne Vinegar: a much more delicate light taste than apple cider vinegar
White Wine vinegar: some say when they use white wine vinegar in place of rice vinegar they add a scant amount of sugar as it is not as sweet tasting.
You could also use lemon juice or lime juice in place of vinegar, and vice versa. I avoid citrus for the most part and so I have used vinegar in place of lemon juice on occasion.
Vinegar, like lemon and lime juice is a healthy food. Remember to avoid Malt Vinegar as it is a gluten.