I use a utility craft knife and a ruler. I like to spend my $$ on beautiful papers and embellies and so I try to stay away from expensive tools as they hurt my scrappy budjet. To make the holes I generally sandwich the chipboard pieces between thin wood boards and clamp it all down and drill... LOL! It works really well as long as you don't force the drill and you pull up when it starts getting jammed.
It's probably not good for the blade, but I just use my regular trimmer (the Fiskars rotary desktop trimmer below). If it's medium weight chipboard I need to make a few passes, but it cuts like butter through the lighter-weight cb. I've never cut the really thick chipboard as I rarely use it.