What advisors should a startup have?

Besides a Lawyer and an accountant what other advisors should I have to build a startup? Where can I find advice with things like creating a marketing plan and finding investment?

Find a professional/business mentor.

Start with a small group of potential mentors. Ask 3-4 different seasoned business professionals that you know if you can take them out to lunch once a month to talk shop (this means a weekly lunch meeting for you). The goal is to land one solid long term mentor relationship out of this group. If you don't find a mentor in your initial group, end these lunches and add others until you find a great fit that challenges and stimulates you professionally.

These are NOT relationships you use to help you run your business. If they have the time to help you, they probably aren't the right mentor. These are people who can help you think about macro issues and offer contact points for invaluable resources. They will offer ways of looking at life and business and shape you professionally.

What you owe a mentor in return is sincere gratitude (it starts with always picking up the lunch tab), accountability, and sensitivity to their valuable time. This means follow-through/reporting on every business issue that you discuss.

Advisors if you are not a marketing guy you need advisors for marketing and a company needs lawyer and you can choose other advisors later on while the company grows.

Most important thing is better than hiring advisors discuss your product with as many senior people as possible and try to find the people who are most interested and then get them in to the company rather than hiring advisors.

You can find many worthy people in linkedin groups and also in other social sites.

I'm not sure how things are in your area but up here in Canada there are a number of small business centers and other government / government funded organizations that provide small business with advice, resources and can point you towards funding programs.