There are many job requirements in the field of
* Web design,
* Administrative assistant,
* Data entry, etc.
I would say there more opportunities for content developers and SEO professionals.
Signing up on oDesk as a provider (freelancer) is free. Only buyers pay a fee. All freelancers, regardless of area of expertise, must pass the oDesk readiness test before they can apply for jobs.
There are hourly jobs too as well as on a 'paid to task' basis.