$presets = imagecache_presets();
print_r($presets);

Array
(
    [1] => Array
        (
            [presetid] => 1
            [presetname] => small
            [actions] => Array
            [storage] => 0
        )
 
    [2] => Array
        (
            [presetid] => 2
            [presetname] => full
            [actions] => Array
            [storage] => 0
        )
)

ImageCache 6.x-2.x