The list of primary mirrors:

FileShack:
Jailbreak: Source 0.6 Installer (EXE - 399mb)
Jailbreak: Source 0.6 (ZIP - 568mb)

ModDB:
Jailbreak: Source 0.6 Installer (EXE - 399mb)
Jailbreak: Source 0.6 (ZIP - 568mb)

HL2Files:
Jailbreak: Source 0.6 Installer (EXE - 399mb)

AtomicGamer:
Jailbreak: Source 0.6 Installer (EXE - 399mb)
Jailbreak: Source 0.6 (ZIP - 568mb)

The list of direct downloads.

Dedifrag.com:
Jailbreak: Source 0.6 Installer (EXE - 399mb)
Jailbreak: Source 0.6 (ZIP - 568mb)

ConvictGaming.co.uk:
Jailbreak: Source 0.6 Installer (EXE - 399mb)
Jailbreak: Source 0.6 (ZIP - 568mb)

MegaUpload.com:
Jailbreak: Source 0.6 Installer (EXE - 399mb)
Jailbreak: Source 0.6 (ZIP - 568mb)

InstantRespawn.com:
Jailbreak: Source 0.6 Installer (EXE - 399mb)
Jailbreak: Source 0.6 (ZIP - 568mb)

This is the server files for the current release of Jailbreak: Source.

FileShack:
Jailbreak: Source 0.6 Server Files (ZIP - 360mb)

ModDB:
Jailbreak: Source 0.6 Server Files (ZIP - 360mb)

Hl2Files:
Jailbreak: Source 0.6 Server Files (ZIP - 360mb)

Dedifrag.com:
Jailbreak: Source 0.6 Server Files (ZIP - 360mb)

InstantRespawn.com:
Jailbreak: Source 0.6 Server Files (ZIP - 360mb)

If you're just planning to play Jailbreak: Source, and not host a server, then you're best off downloading the Installer and not the ZIP file. Once the installer has finished downloading, click Run and follow the instructions.

The mod will be installed to your SourceMods directory. Once it has finished installing, you will need to restart Steam! That's it!

If you're planning to run a server, then download the ZIP file, as you'll need to upload these files to your server. The ZIP file also contains the Linux Binaries.