I recently began my own business, and a friend recommended applying for a small business credit card. Though I have been using my personal visa and mastercard, she mentioned there are some cards available with fixed rates which work especially with small businesses. Other than American Express and the other major cards, are there any others out there that may be worth a shot?

If you're planning to pay your balance in full each month, then you'll want the credit card (or combination of cards) that will pay you the most for your expected spending profile. That is, how much you expect to spend on office supplies, gasoline, travel, telecom, restaurants, etc.

The quickest way I know to figure out which credit card will pay you the most for your spending profile, is this rewards calculator:
http://www.creditcardtuneup.com/?card_type=Business

If you're planning on carrying a balance for a while, then there are some business cards with nice low fixed APR (e.g. Advanta). There are also cards with introductory 0% APRs. You can also browse cards via that web site.