I think people who are giving their hard work away are entitled to put whatever conditions on it they like. Loads of the stuff I use is free but only for non-commercial use...seems reasonable to me, if you're making money out of their work perhaps they should get some of it too.
freesound.org has lots of interesting samples. Most is completely free and royalty-free but you'll probably find enough variety of licence conditions to upset you.
http://www.looperman.com/ has many samples/loops etc. but no good for you because some do ask to be credited if used in commercial releases.
And the VST and sample lists at
http://bedroomproducersblog.com/
should give you many more to play with.
Steve