There are good directories and then there are great directories out there...I guess it all depends what you are looking for to make the directory you are looking at good or great! The London Advertising Directory has over 900 links and over 50 categories in many areas of interest.
This site is very easy to search and to find exactly what you maybe looking for...check them out - and decide for yourself. Some of the categories they have are graphics, photography, marketing and copywriting to name a very very few. You can also suggest a link or category while you are there too!