You've probably heard her sing Maahi Ve in Kaante. Deep, and khule gale wali gaayaki. Classically trained, she handles both low and high notes with equal ease. Even though she had already sung several Bollywood songs by then, it wasn't until Maahi Ve that she got the recognition that she deserved. The song was extremely well received, though that may have more to do with its video rather than Richa's voice ;)
Here's arguably her most popular song. Notice how loud she gets in parts without getting screechy or besura. Sukhwinder Singh, the male voice, is another amazingly talented singer, but that's a post for another day :)
One another aspect of her voice is that it oozes with earthy confidence. No sweet nothings or love ballads for her - this woman delivers strong, powerful statements with her songs.
Listen to her in Sajda from My Name Is Khan. She steals the song completely. And that's not an easy thing to do, when you are singing with Rahat.
While one gets to hear her now fairly frequently as part of Hindi film music, I think, her forte is devotional music performed live. This probably has something to do with the fact that she has done this since she was a kid.
Here she charms her audience with Amir Khushro's poetry.
I leave you with this - Show Me Your Jalwa from Aaja Nachle. Her expression is perfect for the lyrics, and her strong voice would fill even the meekest women with self-confidence.
Hats off to a truly "strong" singer!