Best for mostFolger Shakespeare Library · 1994
For almost everyone, the Folger is the right Tempest — facing-page glosses keep the magic, the masque, and Prospero's knotty speeches clear, with scene-by-scene synopses. Cheap, and the classroom standard. This is where I'd start.
Most scholarlyArden (3rd series) · 1999
The Arden Third Series, edited by the Vaughans, is the scholar's Tempest — a long introduction (strong on the play's colonial readings) and dense footnotes. Indispensable for study; more than a first read needs.
For beginnersNo Fear Shakespeare · 2003
No Fear sets the original beside a plain modern paraphrase — a crutch, not the poetry, but a way through if the language has stopped you before.
William ShakespeareThe Tempesttr. Free (public domain)
FreeFree (public domain) · 1623
The Tempest is public domain, so the full text is free — Folger Digital Texts, MIT, Gutenberg. No glosses, but the whole play at no cost.