The other one I can think of is `"` or `'` before and `"` after.

"@andytlr is valid"

'#1', "#1", #1. and #, are valid

"@kevinsawicki's" and '@kevinsawicki's' are valid.

"@andytlr" and '@andytlr' are valid.

@andytlr, is valid. @andytlr. Is also valid.