Our nutritionist actually say that a cup of popcorn (no butter, no salt) is actually great for snacks. Then again, it's like chewing paper cups without them flavors. No wonder she recommends it.
I like to keep a whole bunch of nuts handy. Peanuts, cashews... whatever in a jar so you can munch and crunch on them. I go for the dry roast or plain ones so they're not heavy in oil and fat.
I've been snacking like crazy during work time. It's insane. Coffee breaks are not meant for human consumption. I'm gonna pack on more weight at this rate! Waaaah!