Hi
I have seen both capital and small letters after the exclamatory mark. What is standard? Could you give me a few examples?
PS: Could we also call it exclamation mark?
Tom
Hi Tom
An exclamation mark/point usually comes at the end of a sentence, so the next letter would be capitalized because it would be the first word of the next sentence.
An exception that comes to mind is a direct quote:
“Watch out!” he screamed.
You might occasionally find it in the middle of a sentence for effect (i.e., the next word would not be capitalized), but I’d say that’s much more the exception than the rule.
Otherwise, in very informal writing, you’re liable to find just about anything. 
Amy