Affordable radio slaves?

So for my weddings and special events photography class, we're required to purchase several things. One of those things being a external flash(duh) and a radio slave or sync cord.

Being that it will be my first time working with an external flash, I really don't know what to get.

Can anyone help me in choosing an affordable radio slave with a transmitter and receiver that will work fine?

If not, what sync cord is the best? Does the brand even matter?

This class is going to require a lot of on location and studio shooting so basically the flash isn't only going to be on the camera.

& now that I'm at it, is there a good third party brand where I can find an external flash for a Nikon d90? An affordable one I mean.

If not, i'll stick into buying a sb 600:)

Pardon my ignorance, but the only thing I want is to make the right purchase

The D90 can fire an off-camera SB-600 without a radio popper. Look into "Commander mode" to find out how. You use the pop-up as your master and the SB-600 as the slave. The light trigger won't work more than maybe 50 feet away, but no sync cord can reach more than a few feet anyway.

I'd like to see you get an SB-700 if at all possible. It is infinitely easier to use than an SB-600. You just turn the switch to select master or remote. On the SB-600, you need to push different combinations of buttons to make the selection from menus.

Look in your D90 custom settings menus for "Flash cntrl for built-in flash." Choose "C" and take it from there.

You will want to stick to a Nikon PC cord if you go that route. I use the SC-29.

These were all shot using the commander mode and a combination of SB-800s and SB-900.

I say something about the set-up for many of them.

Why does it have to be a radio slave? Optically triggered slaves are far cheaper*, even the high quality ones. The Vivitar slave is about £10. There's one on UK Ebay - 110937064303 - at that price. This particular slave works with any Flash Gun, hotshoe or PC connected. By using a slave, one avoids a direct connection between gun and camera. This is good because the high trigger voltage of an older gun can fry the delicate electronics in some newer cameras. As for the gun itself, I always end up recommending the vivtar 283 - it is a full system flash with too many accessories to list here but there are filters, filter holders, flash reflector holders, a remote cord that places the auto sensor on the camera not the flash, Thyristor 4 stop auto-sensor, Varipower sensor etc etc etc. There are many around and one could buy three for the cost of one SB600.
There's a good write-up on these at http://www.theothermartintaylor.com/moveabletype/archives/cameras/000156.html. Just note that consumer demand has kept this gun in manufacture for 37 years!
If all you want is raw power without the control systems of the '283 then there are 1000s of very cheap 100+GN guns out there, often fully manual so you'd need to learn how to set your camera to the flash 'cos the gun don't adjust to suit your camera! With a dSLR you can quickly see the effects of what you've done so this needn't be too difficult.
*But not necessarily a bargain. The cheaper Hong Kong/China/Korea ones are unreliable and can trigger the flash for no good reason - annoying if there's a ten second recycle time!

SB-600 is an awesome flash. Have 5 of them.

If you want to control them, yes you can use the Nikon Trigger, but its line of site and in my opinion weak especially at weddings or receptions. You best bet if you want to start out is Cowboy Studios System. Can't beat the price.
Its no Pocket Wizard but it lets you start out and get a good understanding of trigger/receivers.
-FamZing Photography & Video - Upstate Wedding Photographers