Encrypting a single file with password and keyfile

I am a fan of TrueCrypt and I guess it's the best encryption tool available. As far as I understand, TrueCrypt created encrypted containers which acts a place to store files.

I would like to encrypt a single file. Preferably with a password and a special key file (like in TrueCrypt).

It would be great (but not mandatory) if the file doesn't require any third party software to encrypt and decrypt, in the sense that I provide the password and key to the file directly.

You can always use the openssl command line utility, works on all OSs.

check http://tombuntu.com/index.php/2007/12/12/simple-file-encryption-with-openssl/ and http://www.dslreports.com/shownews/Encrypt-files-quickly-with-OpenSSL-87586 for examples.

Use AxCrypt.

I would like to encrypt a single file. Preferably with a password

AxCrypt only encrypts single files. You can encrypt multiple files at once, but they are each encrypted separately (with the same password if you wish to do so).

...and a special key file (like in TrueCrypt).

AxCrypt can also generate key files.

It would be great (but not mandatory) if the file doesn't require any third party software to encrypt and decrypt, in the sense that I provide the password and key to the file directly.

AxCrypt gives you the option to create a self-extracting .exe file instead of a typical encrypted file. The self-extracting .exe file will not need AxCrypt to be installed in order to decrypt, but it will obviously still require the password or key file to decrypt.