http://eclipse.org
http://kdevelop.org
i use eclipse for java .. there is also the netbeans ide that comes with jdk, i have used it and it is very good as well.. but i would recommend eclipse..
eclipse also does c++ with a plugin, i believe it is called cdt ? i have never tried it. in c/c++ i prefer kdevelop for large projects and kate for small projects..
there are lots more ides out there and you will get a dozen opinions on this subject and the only way to know which one you like is to start downloading and installing.. after all, they are free..