See the split page for details about UTF8 encoding
Unicode.org in its charts section offers useful links to the Unicode code charts. The only problem with it though, is that the code range of each subset is not listed there, so if you already have a rough or precise idea of the code you're looking for, their set of links is difficult to use. Therefore, I present similar links here, which do show the starting point of the code range.
See also my font tester.
BabelMap by BabelStone is a very handy Unicode tool for Windows. Works well in Wine under Linux too.
See also Basic Multilingual Plane in Unicode.