The best way is producing the photo that you need by yourself but not everyone is able to do that. Better no photo than a ugly one! What to do in those cases?
Fortunately there are a lot of website specialized in distributing, for free or for a cheap price, all photo that you need.
I’ll list here several of them for your inspirational use.
Always remind to yourself of checking the right of use, the license on the photo. Some pictures could be free for any use, some others just for personal and not for commercial use. Other artists just require a link back for attribution. Pay attention to that and…good pictures!

http://www.gettyimages.com/

http://www.shutterstock.com/
If you sign up an account they allow you to download the photo and the vector image of the week for free.

http://www.istockphoto.com/SXCoffer

http://it.fotolia.com/

http://www.stockvault.net/

http://www.bigstockphoto.com/

http://www.photos.com/en/

http://www.crestock.com/

http://www.veer.com/

http://www.dreamstime.com/

http://www.pixmac.com/

http://depositphotos.com/
Free use of the photos (link back and attribution required) for your blog

http://www.freefoto.com/index.jsp

http://www.freeimages.co.uk/
Free both for personal and commercial use

http://www.imageafter.com/index.php

http://www.morguefile.com/
Other stock photos

http://www.jupiterimages.com/

http://www.oneeyeland.com/stock.php
Please, if you know any other good photo source leave a comment to the post. Thank you!