At Hyperpolyglot compare PHP, Perl, Python, Ruby and more side-by-side.

Rosetta Code is a programming chrestomathy site. The idea is to present solutions to the same task in as many different languages as possible, to demonstrate how languages are similar and different, and to aid a person with a grounding in one approach to a problem in learning another. Rosetta Code currently has hundreds of tasks, and covers over 150 languages, though we do not have solutions to every task in every language, Python is very well represented.

Several in 2006, David Howard's http://web.archive.org/web/20100420080552/http://www.dmh2000.com/cjpr/. This essay provides implementations of moderately simple algorithms, like Red-Black Trees in various languages. The essay compares language features and renders fair verdicts. It has a handy feature to scroll through the various implementations side by side. A good, quick read.

Several in 2002: GlyphLefkowitz wrote, and MikeConnell updated some very simple performance benchmarks. This is no longer being updated.

Several in 2000: Lutz Prechelt's article An Empirical Comparison of C, C++, Java, Perl, Python, Rexx, and Tcl for a Search/String-Processing Program (pdf) is a little old, but it is REAL RESEARCH, comparing productivity and program performance for 80 different implementations of the same requirements, in seven languages.

Several in 1997: Guido's essay Comparing Python to Other Languages is an essay comparison of Python to Java, JavaScript, Perl, Tcl, Smalltalk, C++, Common Lisp, and Scheme.

erratically updated: "Bilateral comparisons of scripting languages"

Important: this reply to Forrester Research's 2007 Survey on Dynamic Languages

The PLEAC - Programming Language Examples Alike Cookbook. This project aims to gather fans of programming, in order to implement the solutions to the programming problems from the Perl Cookbook in other programming languages.