The current view on the politically correct way to refer to a person with a disability is to refer to the person before the disability. This is referred to as Person First Language.
Examples:
A blind person is now A person who is blind.
An autistic child is now A child with autism.
The dyslexic are now People with dyslexia.*
Person First Language is often harped upon by people who are trying too hard to be politically correct, but it is generally accepted and used by professional is all fields (educators, OTs, SLPs, etc.) You may not notice it, as most people are generally not militant about it, but it is there.
Part of the reason for Person First Language is to remove the semantic difference between severe disabilities and minor ones. You already say 'he wears glasses' or 'she uses a hearing aid', but when talking about a mental deficiency or severe physical disabilities we automatically switch it around ('retarded child', 'deaf person'). This is sometimes contrasted as the difference between 'to be X' and 'to have X'. There is no good reason to say a person is their disability.
There are some other changes that go along with the Person First Language philosophy. For example, if there is no need to mention a disability, it should not be mentioned. 'Need' is loosely defined, but in general one should avoid speaking as if an individual's disability were the most important or notable aspect of that person; when asked "what is Chris like?," your first response should not be "well, he's in a wheelchair." (It might still be acceptable to use that as an identifier of sorts, if you are trying to pick Chris out of a crowd, but a disability shouldn't be used to describe someone's personality).
Some words that you are supposed to avoid are 'lame', 'cripple', 'deformed', 'invalid', 'handicap'**, and 'normals' (for example, 'normal speakers', in contrast to someone who has a speech impairment). Also be careful when using words like 'victim', which suggests a need for sympathy, and 'patient', which implies sickness. Some people also advise that we drop idioms such as 'blind faith', 'turn a deaf ear', and 'lame excuse'.
Some people... As you've no doubt noticed, some of these go a bit too far. The guiding principle with Person First Language is to speak in a way that doesn't make people uncomfortable with disabilities (their own or another's). If you start making a big fuss over all this, or if your speech sounds stilted and contrived, you're not helping. It's more important to pay attention to how your words affect others than to follow all or any of these principles. The central 'good idea' of person first language is up there in the first paragraph. For the rest of it, just try to be aware of how your words shape perceptions.
* A notable exception to this is the Deaf community. This is an exception to the rule in part because the Deaf (yes, always capitalized) community has chosen it as a label for themselves. It also gets bonus points because it's less awkward and shorter than 'people who are deaf'. Person First Language isn't intended to be awkward; if you cannot format a grammatically pleasing sentence using PFL, it's usually acceptable to use more natural speech patterns. On the other hand, you are supposed to try to use PFL whenever you can.
** Most people don't understand why 'handicap' is bad, and 'disability' is good. (Neither do I, really). But if you're spending much time around people working with people with disabilities, you'll find that handicapped is out, and disability is in. In part this is because 'handicapped' is the word that we used when we weren't so enlightened (compare today to the 1950s, and you'll see why we want to divorce ourselves from that). Also, 'handicap' is often defined specifically as environmental obstacles imposed by society upon individuals, not as something intrinsic to the individual.