JPL Planetary and Lunar Ephemeris DE422 for the jplephem package.
This is the most recent long-period ephemeris published by the Jet Propulsion Laboratory. While requiring more than half a gigabyte of space, it achieves quite high accuracy.
|Name:||DE422 (September 2009)|
|Years:||-3000 through 3000|
|Report:||Jones, Fomalont, Dhawan, Romney, Folkner, Lanyi, Border, Jacobson (2010) [PDF]|
This ephemeris incorporates ranging data from recent spacecraft missions, including the Cassini mission to Saturn, which results in an accuracy for Saturn of a few milliarcseconds for positions over the past decade. If this ephemeris is too large for your application, take a look at DE421 and DE423 as alternatives.
To compute using this ephemeris in Python, see the jplephem package.