I love handlebar bags! It's like having a convenient dashboard and glove compartment on the front of your bike.
My main handlebar bag is less conventional than some: It's a Rivendell/Baggins Hobo bag. I saw one recently available on eBay, by the way. The main compartment is huge, and the smaller pockets that face you as you ride are really convenient. I always keep a digital camera in one pocket; cell phone, wallet, and keys in the other. The main compartment easily holds all kinds of stuff. I keep a compact pump in there... as well as hat, gloves, and sometimes a light jacket. Sunscreen and sunglasses as well. Maybe a book or magazine if I'm going to stop somewhere during a ride or commute. The main compartment will even hold a DSLR camera with a small to medium lens attached. So it's a big bag. The only downside is that this particular bag swings a lot if you get out of the saddle on a climb or sprint. I don't recommend it for a bike that you do a lot of out-of-saddle pedaling on. A smaller handlebar bag, or a more rigidly supported one, would be better.
There are some photos here:
http://www.pbase.com/sean000/bicycles
The smaller Candybar bag on my wife's bike is also quite nice. I've ridden with that on my racing bike. It's so small that it doesn't swing much, and there are loops so you can anchor it to the brake hoods or bars.
Of course there are plenty of conventional cordura bags out there. Ortlieb makes some good ones. I do like the waxed canvas bags though. Others may not.
Sean