I have an SB-600 which im totally in love with. I also have the SU-800 remote commander, and im hoping to pick up another SB-600 in the next few weeks The SB-600 has an internal zoom head so it will shoot out a flash that is just a bit larger than the viewable area on your lens which is pretty sweet.
not really sure on the meaning behind Directional Flashes, all flashes are directional. I have a diffuser cap that i can put on my SB-600 to make it omnidirectional if need be.
CJ my "cohort" has an equivelant setup in Canon, this is the remote commander.
http://www.amazon.com/Canon-Speedlit...9089103&sr=1-1
As for a speedlight he runs with this
http://www.amazon.com/Canon-Speedlit...9089192&sr=1-1
its pretty burly, if you are holding it and it does a full flash discharge you can feel the thing buck. lol. my SB-600 does too but not as much.
this shit is pricey, but if you want off camera you gotta pay the piper unless you want to go with a cabled setup with PC cables. That is probably the cheapest setup.
I spent $400 on my Sb-600 and Su-800 commander.
You can also go with setups like pocketwizards and cybersyncs, but they are pricey as hell. You are looking at $600 for the transmitter, 2 recievers, and no flashes.
The Nikon CLS DOES work noticable better than the Canons flash systems, it just works so damn well. The Canon Setup is not bad by any means, but it takes CJ longer to get his Dialed in than it takes me.
Both the Commander and the Speedlight have built in autofocus lights that stomp any on-camera autofocus light. With the SU-800 on my D40 i can very accuratly focus on anything even in pitch black.
the only thing that sucks about either of these systems, is they run off line of sight. So if yer outdoors you cant have the flash more than mayve 40 feet away, and you have to make sure it is positioned for direct line of site.... Indoors in small and medium sized rooms the IR bounces off fucking everything, so you can almost put the light behind the couch and it will still fire off. if i were you i would definatly run with Canons Speedlites over anything else. they are engineered to meter with the Canons so they take most of the guess work out of the way.
Even without the commander, if you slap that 430EX on your camera you will notice a HUGE improvement. Bouncing the light indoors almost always yields perfect lighting, and they work great for fill flash for outdoors if it is a cloudless day.