SPOJ - Sphere Online Judge

First of all, an Online Judge is a system that tests your programs with different inputs and checks whether the outputs of your program are true. Online Judges generally used for programming contests, however you can use some of them for practice.
SPOJ is a popular Online Judge System. It has ~90000 registered users, ~8000 problems and you can use ~40 programming languages. You can discuss the algorithms below the problem-texts and in the forum with other members.
I am sure if you are interested in algorithmic problem solving, then you will enjoy it!

Supported Languages:

C++ C++ (g++ 4.0.0-8)
C C (gcc 4.3.2)
PAS Pascal (fpc 2.2.4)
C++ C++ (g++ 4.3.2)
JAVA Java (JavaSE 6)
PYTH Python (python 2.5)
C99 C99 strict (gcc 4.3.2)
PERL Perl (perl 5.12.1)
C# C# (gmcs 2.0.1)
RUBY Ruby (ruby 1.9.0)
HASK Haskell (ghc 6.10.4)
BF Brainf**k (bff 1.0.3.1)
PYTH Python 3 (python 3.1.2)
PAS Pascal (gpc 20070904)
PHP PHP (php 5.2.6)
CAML Ocaml (ocamlopt 3.10.2)
ADA ADA 95 (gnat 4.3.2)
BASH Bash (bash-4.0.37)
LISP Common Lisp (clisp 2.44.1)
LISP Common Lisp (sbcl 1.0.18)
D D (gdc 4.1.3)
LUA Lua (luac 5.1.3)
ASM Assembler (nasm 2.03.01)
SCM Scheme (guile 1.8.5)
JAR JAR (JavaSE 6)
FORT Fortran 95 (gfortran 4.3.2)
GO Go (gc 2010-07-14)
PIKE Pike (pike 7.6.112)
ERL Erlang (erl 5.6.3)
SCAL Scala (scala 2.8.0)
PRLG Prolog (swipl 5.6.58)
WSPC Whitespace (wspace 0.3)
ICON Icon (iconc 9.4.3)
TCL Tcl (tclsh 8.5.3)
F# F# (fsharp 2.0.0)
NICE Nice (nicec 0.9.6)
NEM Nemerle (ncc 0.9.3)
SCM Scheme (stalin 0.11)
ICK Intercal (ick 0.28-4)
ST Smalltalk (gst 3.0.3)
JS JavaScript (rhino 1.7R1-2)
CLOJ Clojure (clojure 1.1.0)
CLPS Clips (clips 6.24)
PERL

44 programming languages.

BTW, you can not use some languages for some problems.

SPOJ - Sphere Online Judge
http://www.spoj.pl/