Check this article from the SL wiki: Guide to Jobs in Second Life [UPDATE: It's not possible to bookmark SL wiki pages, however a link to the article can be found on the page that this link takes you to.]
Try Search from with your viewer, select the Classifieds tab, and then Employment from the drop down box.
Check the Employment Ops & Help Wanted section on the SL Forums
SL Exchange's forum also has an employment section. (Use Ctrl-F and click on the Classifieds tab. Search Employment.) [Update: direct link here; SL Exchange is now called Xstreet SL]
Another SL jobs forum: SLJobfinder.com
Inworld there is Job Island http://slurl.com/secondlife/Job%20Island/128/128/22 which also has a website (which about gives the measure of things I think, though there is a weekly newsletter that you can sign up to from a board inworld).
Book: The Entrepreneur's Guide to Second Life: Making Money in the Metaverse by Daniel Terdiman
Book: How to Make Real Money in Second Life: Boost Your Business, Market Your Services, and Sell Your Products in the World's Hottest Virtual Community by Robert Freedman
If all else fails and you simply want a few hundred Lindens in exchange for a dollar or two, then click on your account balance (in the top right corner) to be connected to the LindEX currency exchange on the second-life website.