Knives are, arguably, the single most important tools in the kitchen. I can cook on crappy pans (though I don't like to), but I refuse to work with crappy knives. Most cooks will get animated on the subject, whether expounding the virtues of Henckels vs. Wusthof or waxing rhapsodic over their favorite blade that they've had since college days. (See Apartment Therapy's series on the matter. Gotta love that samurai knife!) Everyone has their own opinion on what knives and which brands to buy. If you're starting from scratch, BillyKnowsBest recommends the Henckels 5-Star starter set.
My one go-to knife, the blade I pick up first for most things, is the 7-inch santoku from Henckels 4-Star (pictured). I like the length of the blade, the subtle curve and the ergonomic handle. It's great on vegetables, yet still has enough width and heft to smash garlic or cut through chicken bones. I of course also use a 4-inch paring knife (also Henckels) when a small blade is called for. I also use an 8-inch utility knife with the same ergo handle for making long, even cuts, as on tuna steak, and a long serrated knife (this one's Wusthof) that's equally good on crusty bread and soft tomatoes. But if I were trapped on a desert island with just one knife, it's the santoku all the way.
Come to think of it, we're overdue to have the knives sharpened. Both Drewe's Brothers (1706 Church St) and Cook's Boulevard (1309 Castro St) offer sharpening services, but they send it out so there's a 2-3 day turnaround. If you want prompt, professional service, make an appointment at Jivano's (3674 18th St; 415/552-7997). You can pop into BiRite or Tartine while you wait.