The Shasta brand is good. It can be tricky making dosa — you can watch You Tube videos for tips.

Thank you all! I am going to give some of these a try, I absolutely love any kind of yogurt especially the sour kind.

If I can find batter in the refrigerated section I'll try that as well!

Yes, regular plain yogurt is fine. Try to use one that only has milk and active cultures. No pectin, gelling agents etc.
A lot of those recipes were devised to use up day old yogurt which tends to be more sour than freshly made. The slight tang adds to the flavor and rise of the finished product.

You would use plain yogurt.
The dry mixes are good but I tend to prefer the prepared idli and dosa batters sold in the refrigerated section.

I was recently at the local Indian market getting some ingredients and I noticed a bunch of these pre-packaged mixes for things like savory pancakes that looked SO good and I'm hoping to try my hand at making them. Question - a lot of these called for "sour curd" to be added to the mix. Does that mean just like yogurt / dahi? Or something else? I know sometimes soured yogurt might be used, like in a rasam recipe, but I wasn't sure about the "curd" part.

TIA!!!!