a cable or wireless triggers
a model, background
reflector
a camera
a lens...
and an imagination
One of these would be the ultimate:
http://www.speedgraphic.co.uk/prod.asp?i=2928&1=Canon+ST%2DE2+Speedlite+Transmitter
£153, but worth it as it gives full TTL capability, and can control more than one speedlight should you ever need it. I have one and it's very handy.
not cheap, does it work with the 430EX?
So the Canon Speedlights have a wireless receiver built in?
To start I would go for a 2 foot by 2 foot silver or gold reflector.