WordPress Codex: get_tags()

Retrieve an array of objects for each term in post_tag taxonomy.

Usage

Parameters
$args - The list of arguments that $args can contain, which will overwrite the defaults:

exclude - Default is an empty string. A comma- or space-delimited string of term ids to exclude from the return array. If 'include' is non-empty, 'exclude' is ignored.

include – Default is an empty string. A comma- or space-delimited string of term ids to include in the return array.

number – The maximum number of terms to return. Default is empty.

offset – The number by which to offset the terms query.

fields – Default is ‘all’, which returns an array of term objects. If ‘fields’ is ‘ids’ or ‘names’, returns an array of integers or strings, respectively.

slug – Returns terms whose “slug” matches this value. Default is empty string.

hierarchical – Whether to include terms that have non-empty descendants (even if ‘hide_empty’ is set to true).

search – Returned terms’ names will contain the value of ‘search’, case-insensitive. Default is an empty string.

name__like – Returned terms’ names will begin with the value of ‘name__like’, case-insensitive. Default is empty string.

Return values
(array) - List of tags.

Examples
Displays a list of tags with links to each one and a specific class for each tag:
$tags = get_tags();
$html = '

';
echo $html;

More informations: http://codex.wordpress.org/Function_Reference/get_tags