The Intel compiler produces better code on Intel platforms than gcc. This is not terribly surprising, since gcc is built to support many platforms, but icc can concentrate on just one (well, three, since it also supports EM64T and Itanium, but EM64T isn't a completely different platform).
This freely redistributable package makes use of the Intel compilers and debugger more convenient in several ways. It makes the man pages accessible. It names the C compiler, C++ compiler, and debugger icc, icpc, and idb, regardless of platform. The right version (32-bit or 64-bit) is invoked for you automatically, but you can force the issue with all 3 binaries by passing the -m32 or -m64 flag. This package also exposes the Intel libraries to the dynamic linker so that tricks with LD_LIBRARY_PATH and friends are unnecessary. It installs (X)Emacs support for idb in a place where (X)Emacs can find it automatically. It includes a script named intel-rpmbuild which behaves like rpmbuild but invokes the Intel compilers. Finally, it includes a script named intel-update which automatically adjusts your system to a new version of the Intel tools.
Note that this package does not install the Intel compilers or debugger. It merely exposes them to standard parts of a Linux system.
This is the official home page for intel-extras. (Pathetic, isn't it?) You can download version 2.1 here. Since this package is released under an MIT license, Intel can take the whole thing. Really. Be my guest.