The Folger's and NTC editions are pretty popular, though they aren't necessarily the best.
The Voyager CD is a fine multimedia production featuring video and audio and excellent annotation. It is highly recommended for anyone with a CD drive. The same problems persist, though, with reading on-line.
The Monarch Notes CD-ROM is an excellent general resource for students. Monarch Notes, much like Cliff Notes, provide summaries and analysis of great works of literature. This inexpensive CD offers notes on almost any book you will read during your high school career, including all of Shakespeare's plays. Though many aspects of this CD-ROM appear unprofessional, such as proofreading, interface, and mulitmedia, the sheer strength of the content is enormous. The notes it provides on the play are sufficient for understanding each scene and the play as a whole, though you won't find line by line assistance here.
We were unable to get a copy of this to review but it looks like it might be useful when reading Macbeth or other works.