the meditations by marcus aurelius online

Most of the complete online editions I found are of the translation by George Long (1862)

• Harvard Classics
• Internet Classics Archive, MIT
• Internet Archive plus various other versions at the same site
• as Google PDF
• Audio File

Jeremy Collier (1702) Internet Archive (there are various other translations to choose from)

Meric Casaubon (1634) at Project Gutenberg.

There are Google Book editions with limited preview, however their (almost complete) introductions might helpful:

• Oxford World Classics 1998
• Penguin Classics 2002 /also 1964

Marcus Aurelius at Wikipedia (as usual handle with care)

Image Courtesy Wikimedia Commons, Marcus Aurelius at the Glyptothek in Munich