Good pistol options include the Browning Buckmark, Ruger Mk-II (used, no longer produced), Ruger Mk-III, Ruger 22/45, and Ruger SR22. That last one is the one that most-replicates a self-defense pistol platform (of the Rugers.) Also good handgun choices include the ISSC M22, which is a S/A pistol that otherwise looks and feels like a Glock, and the GSG 1911-22 (of course, based on the 1911 platform.)
For revolvers, look again to the Ruger line, with options in the form of the SP101, and the Single-Six (D/A and S/A, respectively.) Good options also come from Taurus (Tracker and 94-22), and Charter Arms (Pathfinder.)
For rifles, S&W makes a .22 version of their M&P rifle that is supposed to be good. I've fondled one and it felt good, but I've never shot it. The Ruger 10/22 is a great all-around platform that has tons of aftermarket products available. Check out the 10/22 sections on
www.rimfirecentral.com to see how crazy you can get dressing these up. The Marlin 60 is also a great all-time favorite.
I could go one and on, but I'll warn you one thing: you probably aren't interested in just one gun. When you see what's out there, and how easy it is to get hooked on rimfires, you'll be back for more, in just about every platform you can imagine.