anyone know any jobs that i can do based from my current office with no fixed time commitments? web work?

i currently do a job that soemtimes means i will be busy all day but mainly i do about 2 hours work for the 8-11 hours i sit at my desk in the office. is there any work out there that doesnt matter that you cant commit in advance to working any specific number of hours? i would normally be able to commit 20 hours per week, possibly more. the work would ideally be based on using the internet or word processing etc. thanks