depends on where you live.... in florida if part or an entire room is used for business then you can write off part of your rent and bills
plus you've got domains, hosting, outsourced work (coding/design/whatever), accountants, lawyers, etc,
plus all the shit you buy (computers, chairs, desks, papers, printers, ink)
hell if you're real good you can write off everything from laundary soap to mcdonalds. find a good cpa and have them sort it out