Undoubtedly the tool I use most frequently, every day, in my own kitchen, is my 8-inch chef's knife. It's hard to get by without an excellent, well-sharpened paring knife as well.
In a perfect world, all of us home cooks would be experts with a whetstone and a honing steel. And indeed, in culinary school, we were trained to do just that! I'm committing a bit of a sin then by telling you here that I regularly (and very carefully!) use my favorite electric knife sharpener, the Chef’sChoice Trizor XV EdgeSelect Professional Sharpener.
ALWAYS READ THE INSTRUCTIONS, and sharpen with caution! Having knives that are properly sharpened is much safer when slicing ingredients in the kitchen compared to dull ones that don't do the job. It is worth the investment to keep your tools in good working order!