Building a SciFi/Fantasy Library discussion

My sister asked me if I could recommend a sci-fi book that was something similar to Anne McCaffrey's Pern series - in that it's about explorers. I couldn't think of anything. Anyone here have any suggestions?

To Your Scattered Bodies Go by Philip Jose Farmer

All the members of human civilization (and pre-civilized humans too) who have ever lived and died find themselves resurrected on the banks of a massive planet-spanning river where they do not age and if killed they come back to life along some random part of the river. The first book follows a small group who band together and attempt to discover how they got to this strange place by finding the mouth of the river.

Rendezvous with Rama by Arthur C. Clarke

A crew of contemporary astronauts attempt to explore a massive alien artifact as it travels through our solar system.

At the Mountains of Madness by H.P. Lovecraft

An Antarctic expedition stumbles upon the ruins of a lost alien civilization.

Ringworld by Larry Niven

A group of various humans and aliens explores an apparently abandoned alien colony, which in this case takes the form of a massive ring shaped structure encircling a star.

Journey to the Center of the Earth by Jules Verne is about exploring the inside of the earth - but I hesistate in saying so because I can't really "recommend" it, I thought it was especially boring.

Tad Williams Otherland series starting with Otherland (Volume 1 - City Of Golden Shadow). Lots of exploring though I think the author needs a good editor. Great ideas though.

Another Anne McCaffrey series, Dinosaur Planet and Dinosaur Planet Survivors.