Jack Lynch has a comprehensive web site with many online editions of texts by and about Johnson. You will also find portions of Lynch's recent dissertation on Johnson and general material about him, in addition to links to other relevant web sites. Of particular interest is the page about Johnson's Shakespeare edition, and there's a bibliography here of criticism of Johnson's work on Shakespeare.
An extract from novelist Fanny Burney's diary relating how she met Dr. Johnson at a dinner party. The bibliographical reference is not clear from this web site, but the extract is amusing.
In the moo, you can go to The Tabard in Southwark and have a chat with Dr. Johnson (whose role is played by a bot). The Johnson bot is programmed to respond to words in what you say, using citations from Johnson's writing. You'll need to log in to the moo (if you don't have a character at cmcMOO, log in as "guest" and leave the password field blank) and you can type "@go tabard" to get to the inn where Johnson is usually found these days.
Boswell, James. 1791. Life of Johnson. [available online]
Johnson, Samuel. 1765. "Preface to Shakespeare" [available online]
Johnson, Samuel. 1786. "Notes to A Midsummer Night's Dream." [available online?]
both in Johnson on Shakespeare. 1908. Essays and Notes selected and Set Forth with an Introduction by Walter Raleigh. London: Geoffrey Cumberlege, Oxford UP.
there are also many other editions of Johnson's Shakespeare.