Stock.xchng has nearly 4 million images that can be used free of charge for most projects.
It's at www.sxc.hu
It's now ultimately owned by industry leader Getty Images, so don't worry about the peculiar name and obscure domain that make it sound like a European porn site. It isn't!
Basically, Getty use it as a 'feeder' for one of their paid-for stock image sites called IStockPhoto.com. When you do a search you'll find the first and last row of images presented are actually links to paid-for images on IStockPhoto, but all the images in the middle are free to use. You still need to read the licensing requirements for each image, of course. Usually, however, contributors don't place any onerous demands on users. The most common requests are a thank you credit, or simply to let the photographer know where you have used their image.
There are a surprising number of good images available. It's a very useful resource, and perfect for sourcing 'safe to use' images for tight clients who don't want to spend money on images. Give them the web address and tell them to search for images they like.
It's very unwise to use images found via Google unless you definitely have permission to use them. There are many threads on this forum detailing the problems people have had when they used images that turned out to belong to companies like - and here they are again - Getty Images. Demands for thousands of dollars are often reported, and offering to remove the image doesn't make the lawyers disappear. The argument is, you used a paid-for image without paying, so now you must pay for it. Fair enough, too.