Say "Hello" to the world in ASCII art

Perl 5.10 - 195 198 202 203 characters

Here's an entry that does not require any libraries beyond basic regexp matching. The encoded string is 131 characters, and the code to decode and print it takes up 64 characters (assuming no newline at the end of the source). The idea is to represent common 3-character strings by lower case letters.

s!!xfefxxf\t\t\tf efyx
no| cnocfxefxceyxm|xmn
nm|wtnwtgt/uvy \\| 'ym|w`o|
pepyy/o| _ogrr/ _opn (ml
l lbyly|by( )fiihyjm lb,y_
\t\tf |/!;s!\w!substr'(_)\___   \_/|_| |  V \ / _',-95+ord$&,3!eg;say

The encoder is a lot longer and unfortunately not very readable right now. The basic idea is to use dynamic programming to find the shortest encoding for each line, given a fixed set of string substitutions. The string of substitutions on the last line was built by trial and error, and it is possible that another string of substitutions might lead to a shorter program than above.

One trick here is that some substitutions are shorter than 3 characters long: due to the way perl substr works, x is replaced by ' _' and y by '_'. The latter is necessary because \w in the regex matches '_', which is then replaced by '(_)'.

Brainfuck - 862 characters:

>++++[<++++++++>-]>-----[<---->---]<+++>>--[<+>--]<---<<.>.<...>.<....
..>.<.>.<.............................>.<.....>.<.>.>>++++++++++.<.<<.
>>.<<.>>.<<.>>.<<.>...>.<<.>>.<<.>>.<<.>...<....>..<......>.....<..>.<
.>..>.<<.>>.<<.>..>.<<.>>.<<.>>.>.<.<<.>>.<.>.<<.>>.>>>-[<->+++++]<---
-.<<<<.>.<.>---.+++<.>>.<<.>>.>>.<<<<.>.<.>---.<...>.<.>.<.>>>>.<<<.<.
>>>>.<<<<.>>>>.<<<<.>+++.<.>---.>.<<.>>>>>>---[<+>+++++++]<++.<<<<+++.
.>.<<.>>.>>.<<<<.>.+.-<.>>.<<.>>.>.<.<<..>.<..>>.<<..>..>>>.<<<<.>>.<<
.>>.<<.>>>>>+.<<<<.>>>>+.<<<<<.>>.<<...>---.<.>------.<..>.<.>>>>.<<<<
.>>>>>-.<<<<+++++++++.>>>>+.<<<<<.>>.<<.>>.<<..>>.<<.>>.<<.>>>>>-.<<<<
.>.<<.>>.<.>.>.<.<.>.<<.>>.<.>.<---.+++...>.<.>.<.>.<---.+++...>>>>.<<
<<<.>>>>>+.<<<<<...>---.+++.>>>.<<<---.+++.>>>.<<<<.>---.+++...>>>.<<.
<.>.<<..>>.<.>.<---.+++..>>>>+++.<<<<.>>>>----.<<<<.>>>>+.<<.<<<......
..............>>.>>.<.

Python (2.x), 194 characters

print'eNo9T8ENxCAMe5cp/DsqVco2fSH5BsnwZ4ccEIhxbAIgAK9KvDRwGBEjsSfJA6r2N7EISbmrpbLNKFRYOABaC6FAEYkPW/Ztm1t7Z1S3ydtHuV4ooolEV6vPyJ2XH8kGE7d9DAVMhFUte6h7xv5rxg8sf0Qc'.decode('base64').decode('zip')