Here is a list of 50 sci-fi classics you may want to check out.
Please note there is a mistake in the list. The second to last book on the list is actually titled "Who Goes Here?" by Bob Shaw, not the classic "Who Goes There?" by John Campbell (which was actually made into a film - The Thing).

http://www.theregister.co.uk/2011/04/19/sci_fi_poll/