There are a million great uses for a mandolin, but my favorite is for slicing garlic. When you slice on the mandolin rather than by hand, the flavor stays in the garlic rather than on the cutting board and you get perfectly even pieces which makes cooking with it so much easier.
Bench Scrapers are used a lot in baking, but I love having one around for picking up chopped herbs or diced vegetables, cleaning off counters and cutting casseroles or lasagnas into equal portions thanks to its square blade.
There's no other way to zest citrus and I also love to use a icroplaner for grating hard cheeses.
Serrated knives are best known for slicing bread or bagels, but I use mine for everything from slicing tomatoes to taking the skin off vegetables such as eggplants and winter squashes as well as melons. The teeth do a great job of gripping so it's a much safer way to slice and peel.
Rubber cutting boards are found mostly at restaurant supply stores and I can't recommend them highly enough. They won't crack, splinter or chip, don't absorb odors or liquids, are antibacterial and are much easier on knife blades than any other cutting surface. Make sure to get one large enough so that you have enough space to chop and prep.
A large roasting pan does so much more than just roast. You can sear meat in it on the stovetop before roasting, you can braise in it, roast in it or make lasagna in it. It's a true workhorse.
Forget fancy spice grinders - a cheap coffee grinder is all you need to grind spices. Especially great for grinding black pepper to use in your salt and pepper mixes.