I think you've all about covered it. I would also recommend the 'Stainless Steel Rat' series, and even the newer ones are still fairly good. There are other Harry Harrison books not mentioned yet - 'The Technicolour Time Machine' being one.
The 'Red Dwarf' Books are based on the series, but do depart from it a little. They are certainly worth reading.
Robert Rankin - I only read 'Armagedon - The Musical' and I didn't find it that funny - I think his titles are funnier than the books themselves.
There are always 'Bored of the Rings' and 'Barry Trotter' if you like spoofs.
The 'Red Dwarf' Books are based on the series, but do depart from it a little. They are certainly worth reading.
Robert Rankin - I only read 'Armagedon - The Musical' and I didn't find it that funny - I think his titles are funnier than the books themselves.
There are always 'Bored of the Rings' and 'Barry Trotter' if you like spoofs.