The best way to cut a laminate countertop is with a large stationary saw with 12- or 14-inch blades. Alternate methods are to use a jigsaw with a specialized laminate cutting blade or a circular saw with a shop-built jig to guide the cuts.
It is important to use a laminate cutting blade, as it cuts only on the down stroke to minimize chipping of the laminate. To cut laminate in a space with little room to maneuver, use an oscillating multi-tool with a fine-tooth blade. As with any construction task, be sure to measure carefully prior to cutting to get the best fit. Freshly cut laminate has a sharp edge which may be smoothed with 220-grit sandpaper.