Erasmus published five editions of his Latin-Greek New Testament, with annotations, in 1516, 1519, 1522, 1527, and 1535. Gradually, all these editions have become available online.
The Swiss e-rara.ch has Erasmus’ Novum Instrumentum omne of 1516, with the Annotationes.
Navigation is easy, and the site’s table of contents is extensive (though not as exhaustive as to contain each NT book or even chapter). The quality of the images is good. From the contents page, one can download PDF files of parts of the book.
The only drawback I can see for now is that one cannot download a PDF of the entire book, as is possible with the digital collections of the Bayerische Staatsbibliothek.
There is also a GB version of the 1516 edition.
Erasmus’ second edition of 1519 with the Annotationes is not (yet?) available at e-rara, but at the University of Jena; it can also be downloaded as PDF.
It is possible to make links to specific page views, e.g. Erasmus’ conjecture φθονεῖτε at Jas 4:2, for example (and his annotation on the reading).
Erasmus’ third edition of 1522, with the Annotationes, is now available as well at e-rara.
Erasmus’ fourth edition of 1527, with the Annotationes, is now available as well at e-rara.
Erasmus’ 1535 edition can be found at the Erasmus Centre for Early Modern Studies, but only the New Testament text, not the Annotationes, and only in DjVU format.