Can't afford a jointer yet? Here's one great alternative.
If you buy lumber pre-planed to thickness, your craving for a jointer probably pops up only when it comes time to edge joint boards. Here s a method for making perfect edge joints with a router and 1/2" straight or downcut spiral router bit.
(Note: The router bit is cutting in both directions at the same time, making it grabby during this operation. Proceed with caution and remove as little material as possible on the climb-cutting side.)
Clamp the boards you want to join to the jaws of a clamping workstation (such as a Workmate), leaving 1/4" or so of the workpieces overhanging the jaw opening. Close the jaws until the boards are edge to edge, and make witness marks across the joint. The straightedge is set to remove less than 1/32" from the right-hand board.
Open the jaws of the workstation so that the gap between the workpieces is parallel and 7/16" wide. Rout the mating edges of both pieces with one pass of your router, guiding it along the straightedge. Both sides of the cut will match as long as you align your witness marks when gluing up the assembly.