The Time Ships

I'm currently working my way through Stephen Baxter's Manifold trilogy. His writing is incredibly insightful and psychedelic. I'd also suggest the Time Ships (only authorized Time Machine sequel) and anything from the Xeelee universe. Maybe start with Vacuum Diagrams? David Brin's Uplift series is brilliantly written, and personifies non-human characters wonderfully. Heinlein has been a favorite of mine since I was a kid, and his writing always makes me giddy.

On that note, I highly recommend The Time Ships, by Stephen Baxter. He picks up where The Time Machine leaves off and takes the story into some amazing directions.