Iain Banks 'Culture' books - well written space opera stuff.
Tom Clancy's 'Jack Ryan' series - work as stand alones
William Gibson - the 'Sprawl' and 'Bridge' series of cyberpunk
Larry Niven - 'Known Space' lots of sub series in this one - the Gil the Hand ones work out of sequence but Ringworld doesnt
Jack Vance 'Dying Earth' - classic fantasy books - read in any order