Adobe Photoshop CS5.1, as provided by Adobe.

Download #1: English
Download #2: Eu / Multiple Languages

Compatibility
Architecture: x86 (Intel:Mac)

Multicore Intel processor
Mac OS X v10.5.7 or v10.6
1GB of RAM
2GB of available hard-disk space for installation; additional free
space required during installation (cannot install on a volume that
uses a case-sensitive file system or on removable flash-based storage
devices)
1024�768 display (1280�800 recommended) with qualified hardware-
accelerated OpenGL graphics card, 16-bit color, and 256MB of VRAM
Some GPU-accelerated features require graphics support for Shader
Model 3.0 and OpenGL 2.0