flash

I'm doing a photoshoot for the first time on wednesday, in the ruins of an old castle and I was wondering if I need to get a flash unit?? I have a 450D but I dont want to us the built in flash, because I know I would get that damn outline shadow down one side of my model. I can pick up a cheap...

Right, I'm in the market for a flash unit for my 450D badly! I dont have that much cash to splash. So anyone know of a good flash unit, cheap thats gonna do its job an its gonna last.