This is a very simple plugin for ExpressionEngine 2.0 that allows you to get a category ID from a category URL, i didn't want to pay $10 for this type of plugin so i created this in 2 minutes.

Example of uses:

To get a category ID based on a URL segment:

{exp:swanify_category:get category_url="{segment_2}"}

Optional group_id parameter as category url_title is not unique. 

{exp:swanify_category:get category_url="{segment_2}" group_id="3"}