Pros: very little required to sign up, variety of work locations
Cons: unstable hours that you can't support yourself on forever
Randstad is a staffing agency, meaning that while I am their employee, they actually send me out to various locations that require an extra hand for the day.
I call in on Monday and let them know that I am available for work that week and then wait to hear if there's anywhere that could use a worker for the day.
This is great in that you can work in a lot of places you've never thought of before, but on the other hand, it is extremely unstable. Sometimes you can be continuously working for months at a time, while other times you haven't worked in any number of days/weeks/months.
The actual Randstad staff are nice and helpful, doing what they can to get you work and keep your WHIMIS, etc. up to date.