xclip has now been moved to GitHub  and this SourceForge project exists for historical reasons.
xclip works perfectly.
xclip is small and works nicely
Fast and simple.
I have used xclip for clipboard handling to realize one of the ELinks web browser capabilities under X Windows ( www.compmiscellanea.com/en/elinks-configuration.htm#uri-passing ). It works pretty well. There are probably also other clipboard utilities on Earth, but if one has come to xclip place on sourceforge.net, pondering whether to download / install it - do it, xclip is surely worth it.