For practice you can use the Nikon Wireless CLS. The D700 buildin flash can act as commander, and the SB-900 as TTL slave.
Pro: you can use full TTL capabilities.
Con: range is limited, especially in bright areas. Range can be extended by buying a TTL-Flash-Controller (SB-12?).
Cable is a great start, too: it works very reliable, you can use full TTL, but of course range is limited to cable length.
Simple wireless triggers (like YongNuo RF-602, Cactus V4, Skyports, Radiopopper JRx) are the strobist way, cheap, quite reliable, range is good. Downside: no TTL, instead you need to make all settings on the flash itself.
Pro Wireless triggers (Radiopopper PX, Pocketwizard TTL) will give you full TTL with great reliability and good range, but for a hefty price.
I'd buy a cheap set of radio triggers like the YongNuo RF-602 for learning strobist, and see if this works for you. Of course you need to learn lighting manually for this, but I think this is a good skill to have, even if you are using TTL.
For resources of course have a look at strobist 101 and 102 at www.strobist.com.