Any cereal / pulses can soaked, ground up and used to make Adai. However, Some pulses like red kidney beans (rajma) are toxic when uncooked and should always be cooked.
The Base: See column 1
A cereal alone can be used to make Adai like the Rice Adai.
A mixture of rice and lentils is used for the common Adai.
Use sprouted lentils and we have the Mulai kattya adai.
Use cooked rice and we have the Cooked Rice Adai.
Use yogurt for soaking instead of water and you get Yogurt adai.
A mixture of cereals and pulses can be used to make a cereal - lentil Adai
Finger millet is used to make the Ragi Adai.
Use semolina in place of a cereal and gram flour in place of a pulse and you have the instant Adai, the Rava Adai.
A pulse or a mixture of pulses can be used to make the Lentil Adai (Paruppu Adai).
Flavouring: See column 2
A wide variety of stuff can be used to flavour Adai. Ginger, garlic, curry leaves, red chilies & turmeric are commonly used. You can try any of your favourite flavouring agents in place of traditional ones. Though not traditionally cooked, you can try experiment with Rosemary / Sage / Oregano / Thyme or other herbs.
Additives: See column 3
A variety of additives as listed in column 3 can be mixed in the batter. Shallots, spinach, green chili, herbs are commonly used. Try experimenting by adding chopped nuts or any other edibles to cook your own adais.
And this goes to the Well Seasoned cook's Pancakes on Parade