Some of the forms of agnosia are as follows: Object Agnosia, Simultagnosia, Prosopagnosia,Agnosia alexia, Color Agnosia, Auditory agnosia, Somatosensory Agnosia or Astereognosia.
The above video is from http://galatea.stetson.edu/~mgarzon/video.html. It depicts a person coming to terms with their visual agnosia and how that redefines themselves.
Object Agnosia is inability to recognize objects. Subtypes: Form agnosia: Patients perceive only parts of details, not the whole object.
Simultagnosia Patients recognize objects or details but only one at the time. They cannot make out the scene they belong to or make out a whole image out of the details. They literally cannot see the forest for the trees.
Prosopagnosia Patients cannot consciously recognize familiar faces, maybe including their own. They can describe the face and its expression but cannot recognize whose face it is. They still show bodily emotion to the face (your heart-throb still makes your heart throb). They may recognize a person through another cue, like familiar voice or clothing. It is especially likely after right temporal lobe damage. Experts disagree about the causes of prosopagnosia. It may be object agnosia for specific faces, perception disorder in face perception system or syndrome that causes separation of perception of face and memories associated of the face.
Agnostic alexia Inability to recognize text, such as the image below or what you are reading now.
Color agnosia There is a distinction between color perception versus color recognition. Central Achromatosia refers to deficiency in color perception
Auditory agnosia refers to similar symptoms with environmental, nonverbal auditory cues. This is separate from word deafness which is agnosia connected to auditory information.
Receptive amusia is agnosia for music. Cortical deafness refers to people who do not respond to any auditory info but their hearing is intact.
Somatosensory Agnosia or Astereognosia is connected to tactile sense - that is, touch. Patient finds it difficult to recognize objects by touch based on its texture, size and weight. However, they may be able to describe it verbally or recognize same kind of objects from pictures or draw pictures of them. Thought to be connected to lesions or damage in somatosensory cortex.
All agnosias can result from strokes, dementia, or other neurological disorders. For all practical purposes, there is no direct cure. However, patients may learn to identify things better if information is presented via senses other than the damaged one.
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Forest picture from http://www.vdof.org/images/tree-forest-spring-hdwd-1.jpg
Shape picture from http://www.uni.edu/~burgess/3a.jpg