Old English her "in this place, where one puts himself," from Proto-Germanic pronomial stem *hi- (from PIE *ki- "this;" see he) + adverbial suffix -r. Cognate with Old Saxon her, Old Norse, Gothic her, Swedish här, Middle Dutch, Dutch hier, Old High German hiar, German hier.
Phrase here today and gone tomorrow first recorded 1680s in writings of Aphra Behn. Here's to _____ as a toast is from 1590s, probably short for here's health to _____. In vulgar speech, this here as an adjective is attested from 1762. To be neither here nor there "of no consequence" attested from 1580s. Here we go again as a sort of verbal roll of the eyes is attested from 1950. Noun phrase here and now "this present life" is from 1829.