Since 2010-07-13 PyOpenCL is available in Debian unstable in package python-pyopencl.
Currently the only available OpenCL implementation in Debian is one provided with NVIDIA drivers, so PyOpenCL depends on nvidia-libopencl1, nvidia-opencl-common, and nvidia-opencl-icd. As those are non-free packages, python-pyopencl is placed in the contrib section, intended for free packages depending on non-free ones.
To install it one needs therefore to have NVIDIA graphics card supporting CUDA and to enable contrib and non-free sections in /etc/apt/sources.list:
deb ftp://ftp.MIRROR.debian.org/debian/ unstable main contrib non-free deb-src ftp://ftp.MIRROR.debian.org/debian/ unstable main contrib non-free
(replace MIRROR with your country code).