For first encounters with weird aliens, you should give James White's Sector General books a try-- though it is older material with an older writing style.
For the type of civilizations, try Iain Bank's Culture books, or Peter F. Hamilton's Commonwealth Saga, or Alastair Reynolds' Revelation Space books, or Gregory Benford's Galactic Center Saga books, or Dan Simmon's Hyperion Cantos series, or Charles Stross'eses Singularity Sky and Iron Sunrise. What you are looking for (for the sake of googling) is post-human, post-singularity settings.
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