ASCII Library for Creating "Pretty" Directory Trees?

Is there some *nix tool or perl/php library that will let you easily create directory tree visualizations that look like the following?

www
|-- private
|    |-- app 
|    |    |-- php
|    |    |    |-- classes
|    |    |    +-- scripts
|    |    |-- settings
|    |    +-- sql
|    +-- lib
|         +-- ZendFramework-HEAD
+-- public
    |-- css
    |-- images
    +-- scripts

How about this example from Unix Tree / Linux Tree:

ls -R | grep ":$" | sed -e 's/:$//' -e 's/[^-][^\/]*\//--/g' -e 's/^/   /' -e 's/-/|/'  

That oneliner is pretty cool, I'd recommend using the tree util.

bash-3.2$ mkdir -p this/is/some/nested/example
bash-3.2$ mkdir -p this/is/another/super/nested/example
bash-3.2$ mkdir -p this/is/yet/another/example
bash-3.2$ mkdir -p this/is/some/nested/other/example
bash-3.2$ tree this
this
`-- is
    |-- another
    |   `-- super
    |       `-- nested
    |           `-- example
    |-- some
    |   `-- nested
    |       |-- example
    |       `-- other
    |           `-- example
    `-- yet
        `-- another
            `-- example

13 directories, 0 files

I realize this question was answered ages ago, but I just found this program called tree which is pretty cool too.

See the RecursiveTreeIterator class

Allows iterating over a RecursiveIterator to generate an ASCII graphic tree.

$treeIterator = new RecursiveTreeIterator(
    new RecursiveDirectoryIterator('/path/to/dir'),
    RecursiveTreeIterator::SELF_FIRST);

foreach($treeIterator as $val) echo $val, PHP_EOL;

Output will be something like this (with c:\php on my machine):

|-c:\php5\cfg
|-c:\php5\data
| |-c:\php5\data\Base
| | \-c:\php5\data\Base\design
| |   |-c:\php5\data\Base\design\class_diagram.png
| |   \-c:\php5\data\Base\design\design.txt
| |-c:\php5\data\ConsoleTools
| | \-c:\php5\data\ConsoleTools\design
| |   |-c:\php5\data\ConsoleTools\design\class_diagram.png
| |   |-c:\php5\data\ConsoleTools\design\console.png
| |   |-c:\php5\data\ConsoleTools\design\console.xml
…

exa with --tree does an excellent job:

exa --tree ~/tmp/public/

<dir>
├── aboutme
│  └── index.html
├── atrecurse
│  └── index.html
├── base.css
├── html5
│  ├── cat-and-mouse
│  └── frantic
│     ├── css
│     │  └── main.css