-brand development (created by a professional graphic designer)
-a professionally designed, coded and written website that has SEO friendly text
-a professional copywriter
-and some "stuff"
-at the very least a promo card (also professionally designed) that details info and benefits about your product(s) or services, and a business card. I'd also suggest producing a pdf flyer that you can post via email.
Any basic marketing plan also must include a bit of PR, lots of networking, at least one campaign using direct mail and a decent amount of cold calling, which may or may not include buying a list of prospects (for cold calling or direct mail purposes). If you are not good at cold calling, don't do it! Hire someone who is, like email@example.com or ItsYourCall.com, and you will get sterling results!
Bottom line, this saying is right on the money: If you fail to plan, you will plan to fail. If you do not outline in a very strategic manner all these basic tasks and come up with appropriate funding to cover the actions and the "stuff" you will need to launch strongly, you will end up wasting tons of time and energy for naught. Best of luck with your endeavor!