People,
Well, the most obvious answer to that question would be Geordi, as a main character in TNG. True, he had a device, the VISOR, which compensated for his blindness, but if it was detached, he was blind and helpless, as shown in several eps like Skin of Evil and The Enemy.
Also, as mentioned: the DSN ep Melora, as an allegory on paraplegics and quadraplegics; Dr. Miranda Jones from TOS ep Is There in Truth No Beauty; and Captain Pike in TOS ep The Menagerie.
However, it's also quite clear there are fewer disabled people in the future, certainly those of a genetic kind. But there are many other diseases that they still are working on. Witness the future Captain Picard in All Good Things was supposed to be suffering from the early stages of a neurological disease that sounded a bit like Alzheimer's.
Red Ranger