I am creating a tutorial for jquery and was wondering if there are any public websites, to which i can make ajax requests, that will return json string for a simple list, string, objects etc. Are there any websites like that.
JSFiddle has all the things that you might need.
see here: http://doc.jsfiddle.net/use/echo.html
You should set up your own server to do this, or (as @Neal's answer hints) use jsFiddle's embed feature.
Why? Unless you use JSONP, the same origin policy prevents ajax requests across domains. http://en.wikipedia.org/wiki/Same_origin_policy