March 15 is typically the annual tax deadline for many small businesses in America, and with the sole proprietorships and LLC deadline (April 15), you need all the business tax advice you can get.
The Internal Revenue Service (IRS) has set up a tax page for businesses, including self-employed businesses, which you might find helpful.
And for those of you who work from home, this Publication 587, Business Use of Your Home is invaluable (in PDF format).