Tibet area is a historically banned area to the independent travelers. But there are also some problems in other areas like Xinjiang. Is this area or others apart from Tibet banned for independent travelers? Of course I'm not asking about safety in these areas, but for official blocks to access there.
Yes, there are a few, although they're mostly military or border areas that would not really qualify as tourist attractions anyway, and none are anywhere near Tibet in size. Wikipedia has a partial list.
A few more not listed include the Karakorum Highway to Pakistan and the Jiuquan/Dongfeng space complex and launch center (not so) near Jiuquan, Gansu.
Foreign travelers are usually banned from accessing many rural areas in Xinjiang without permit. However cities and touristic areas can be generally visited without any problem.