Depends on the programs you use, and whether or not you're running a full DE or a bare WM. Most programs use Ctrl+X/C/V, Shift+Delete/Shift+Insert/Control+Insert, and/or highlight/middle-click in various unpredictable combinations.
I've found this to be less of a problem in modern desktop environments (especially KDE, in my experience), since most DEs nowadays feature their own clipboard/buffer management.