Unfortunately there is no real client “only” installer.
What you can do, is to download the ZIP archive of the complete Postgres binaries:
http://www.enterprisedb.com/products-services-training/pgbindownload
and then remove the “server” part from it.
When you unzip it, you get the following directories:
bin doc include lib pgAdmin III share StackBuilder symbols
You can remove the doc, include, pgAdmin III, StackBuilder and symbols directories. As far as I can tell (but I am not sure) the client also doesn’t need the share or lib directories, but you would need to test that. So that leaves only the bin directory.
I think the share directory could be needed for localized error messages in psql but I’m not sure about that.
Inside the bin directory you can essentially remove all .exe files (except psql.exe of course). You can also remove all wx*.dll files, they are only needed for pgAdmin. The libxml2.dll and libxslt.dll are also only needed for the server.
If you do want some of the other client tools, you might want to keep
- pg_dump.exe
- pg_dumpall.exe
- pg_restore.exe
One drawback of this approach is that this requires the Visual C++ Redistributable to be installed. But you can overcome that as well by simply putting the MSVCR120.DLL from some computer where it is installed into the bin directory.
So that leaves you with these files (from the bin directory) that are required for the psql client:
- iconv.dll (libiconv-2.dll in newer Postgres versions)
- libeay32.dll
- libintl-8.dll
- libpq.dll
- msvcr120.dll
- ssleay32.dll
- zlib1.dll
- psql.exe
Of course you can also take all that from an existing Postgres installation without the need to download the ZIP archive.
It is obviously not a real installer, but if you put the cleaned up directory into a ZIP file, you can distribute that and whoever needs it just unzips the archive. Personally I find unzip to be the best “installer” anyway (I also use that to install the Postgres server, the Windows installer just has too many quirks)