Hi!
Does someone know if there are some good free graphics which I can use to create my maps??
I only found some single parts but not enought for a whole game.
Or did someone finish his RPG and give me his tilesets?
Here you can see what I did until now, I made the graphics myself but its not good.
well it all on what you wanna do
legally you cannot use any copyrighted material of course, which, I believe includes RPG maker stuff because thats all stuff from commercial 16 bit games.
so, if you use that stuff and “release” your game, by law, they could sue you. however there are soooo many fan games and the worst I have ever heard was a “cease and desist” - and that only because the games also share the name, like “Megaman: Rofl Edition Fan Game” (not a real game, example =P)
but if you game is mainly for “educational purposes”, you learning to make games, i wouldn’t worry too much at first.
also - whatever you use can be a proxy/placeholder - you can replace it later…
@question: there isnt really that much good “free” stuff. especially when you do real game design, you have an idea how things should look - you never find exactly what you want, of course.
so in case of your game getting big and famous, you can still replace the stuff
opengameart.org comes to mind. Googling for “free game art” is going to give you about as much as I’ve got though 
Watch out for “free” word. Usually all free stuff can be used for freeware, but not all free stuff can be used for commercial.
Add “royalty free” to your search. Stuff that is royalty free, you can use for commercial products without worry. See http://en.wikipedia.org/wiki/Royalty-free
You might want to look into the prospect of making your own sprites and graphics, as using ‘free’ images can be rather risky on a commercial scale. A simple search for ‘sprite making tutorials’ got me this: http://bit.ly/xIEGE9 . Good luck!