For starters - you need to establish a well thought out and budgeted backlinking campaign, if you want to see positive and long term results from the engines.
This is in addition to the keyword rich content you add on a regular basis.

If you are looking to bring traffic immediately, pay per click would be my option of choice. Be careful though. It's much more complex than meets the eye. Do a little research, and start out with small campaigns. Start with alternative engines (ie. Jeeves) rather than starting with Overture and Google if your budget is limited and your keywords are highly coveted. Although there is investment involved, you will usually see a positive ROI if done smart.

My advice is from an SEO prospective. There are millions of other ways to lure traffic to your site.