There's a pretty steady stream coming out in papyri, as can be seen in the pages of the journals The Oxyrhynchus Papyri or Zeitschrift für Papyrologie und Epigraphik. Most of it is very fragmentary, but there are exceptions. And most is not very interesting to the general reader. Some of the biggies, though, are

• A bunch of Origen's sermons on the Psalms, completely intact, discovered in 2012 (not yet published).
• The Derveni papyrus had its first official publication in 2006 (an unauthorised publication came out in 1982, against the will of the curator who had been sitting on it for nearly two decades already at that point).
• Philodemos: publication of Philodemos, based on the Herculaneum papyri, began in the 1700s; but new technological developments in recovering text from lumps of coal led to a bunch of new editions starting in the 1990s.
• Fragments of two speeches by Hypereides in the Archimedes palimpsest, published in 2005 and 2008.
• Sappho: one new poem published in 2005, five stanzas of another new poem in 2014.
• Archilochos: a substantial passage in elegiac couplets that relates an episode from the lead-up to the Trojan War, published in 2005.

Shortly before the 20-year mark (i.e. before 1995) were a few others: the most recently discovered of the Orphic gold tablets, and the new Simonides (large fragments of a poem commemorating the battle of Plataiai, published in 1992).

Edit. Hypereides fragments added.

Less than a year ago we discovered a new Sapphic poem which had been lost for approximately 2600 years.

Sappho was an ancient Greek poet, btw.

The Archimedes Palimpsest is perhaps a good example. While the document was rediscovered and recognized for what it might be in the early 20th century, it wasn't until the late 1990's and early 2000's that it was able to be fully read, using modern technology. It includes the only copies of two works of Archimedes, one of which filled in a major gap in the knowledge of his methodology and explained some of his mathematics, as well as the only version of some a previously known writing in the original Greek.

Thanks guys for all the anser I didn't know the we were still discovering new things, so many years later. I really like the archmedies one.