Six Sci-Fi / Fantasy books buffs should read but may not have done.

Six (Dr Dij’s pick) books (or series) that epitomise the genre that you feel are obscure for one reason or another.
This is to test a contention that afficionados, know their stuff.
How many of these have you read?

Encounter With Tiber -Buzz Aldrin and Stephen Barnes
Ambassador’s Progress – Walter M Williams
Men, Martians and Machines – Eric Frank Russell
Dhalgren – Samual R Delaney
Hellstrom’s Hive – Frank Herbert
Planet Of Adventure – Jack Vance

And what would be in your list?