Whenever I’m building a website for a demo or proof of concept, I like to use nice images, but certainly don’t have the budget to get custom photography or graphic work done. So my saviour is always royalty-free images. I’ve always used stock.xchng, but while flicking through the latest edition of Desktop magazine (I highly recommend this mag as a good source of digital design info), I noticed a few new ones (well, new to me ;)):

• stock.xchng – Very good site with many quality royalty-free images.
• jupiterimages – Another great location of royalty-free images; site is also developed in .NET :)
• inmagine – Very large source of royalty-free!
• photolibrary – A little bit slow to load, but another good source of royalty-free.

Feel free to add any others via comments :)