Filing depends on your age, status (single, married, etc.), total taxable income, etc.
Your cash income is probably considered self-employment since you're talking about 1099s. Self-employment income is listed on line 12 Business income or (loss) of the 2009 version of the 1040 form, for example.
As an example, if you're single under 65 for 2009 income, you wouldn't generally have to file if your income were under $9,350.