If you are a comp/sci student you can download Visual Studio Professional (for free) off of Dreamspark - if you need a 64 bit OS you can get Server 2008 R2 off of there too.

if you are not a student, i think GCC (MinGW on windows) may be able to. Im prettysure you cant cross compile though (meaning to make 64 bit binaries, you must be running a 64 bit compiler on a 64 bit capable OS and CPU).

Visual C++ (other than the free express editions) can compile 64bit directly in the IDE. It does appear that you can compile from the Express edition, using command line compilation. See here

Do you mean I can compile code in 64-bit mode using Express Edition? I thought 64-bit compilation was entirely out of question for Express Edition. I just installed Professional Edition on a 64-bit machine under a 32-bit operating system. How do I proceed to compile my code in 64-bits? Or do I need a 64-bit operating system, too. I still have Express installed on a 64-bit machine running 64-bit Vista.

alright so I tried the steps here

http://msdn.microsoft.com/en-us/library/9yb4317s.aspx

to target my application to 64-bit under both Express and professional editions, bot neither of them had the option of a 64-bit platform under the New Solution Platform Dialog Box

Got it. Evidently the "full" installation didn't include the 64-bit compilers. An update solved the problem. Thanks!