EXE or DLL Image base address

If you are examining an DLL or EXE file on disk, use the dumpbin utility. It in installed with Visual Studio or the SDK.

Example Output of dumpbin /headers:

FILE HEADER VALUES
     14C machine (i386)
       6 number of sections
306F7A22 time date stamp Sun Oct 01 22:35:30 1995
       0 file pointer to symbol table
     1D1 number of symbols
      E0 size of optional header
     302 characteristics
            Executable
            32 bit word machine
            Debug information stripped

OPTIONAL HEADER VALUES
     10B magic #
    2.60 linker version
    1E00 size of code
    1E00 size of initialized data
       0 size of uninitialized data
    1144 address of entry point
    1000 base of code
    3000 base of data
         ----- new -----
 **2BB0000 image base**  <--- This is what you are looking for
    1000 section alignment
     200 file alignment
       3 subsystem (Windows CUI)
    4.00 operating system version
    4.00 image version
    3.50 subsystem version
    8000 size of image
     400 size of headers
    62C8 checksum
  100000 size of stack reserve
    1000 size of stack commit
  100000 size of heap reserve
    1000 size of heap commit
       0 [       0] address [size] of Export Directory
    5000 [      3C] address [size] of Import Directory
    6000 [     394] address [size] of Resource Directory
       0 [       0] address [size] of Exception Directory
       0 [       0] address [size] of Security Directory
    7000 [     21C] address [size] of Base Relocation Directory
    3030 [      38] address [size] of Debug Directory
       0 [       0] address [size] of Description Directory
       0 [       0] address [size] of Special Directory
       0 [       0] address [size] of Thread Storage Directory
       0 [       0] address [size] of Load Configuration Directory
     268 [      44] address [size] of Bound Import Directory
    50A0 [      64] address [size] of Import Address Table Directory
       0 [       0] address [size] of Reserved Directory
       0 [       0] address [size] of Reserved Directory
       0 [       0] address [size] of Reserved Directory

SECTION HEADER #1
   .text name
    1D24 virtual size
    1000 virtual address
    1E00 size of raw data
     400 file pointer to raw data
       0 file pointer to relocation table
    3C20 file pointer to line numbers
       0 number of relocations
     37E number of line numbers
60000020 flags
         Code
         (no align specified)
         Execute Read

If you load the binary into your own process you can use GetModuleHandle. It returns a HMODULE, but that is the same as HINSTANCE and the base address.

If you want to know what base address the binary prefers you should read the PE header. See here and look for the ImageBase field in IMAGE_OPTIONAL_HEADER.

Edit: GetModuleHandle(NULL) will return the base address (altough the specified type is HMODULE) for the current process.