It depends on what your goal is in attaining the knowledge of Martial Arts. If it is to fight in the UFC, you might want to look more at grappling styles like Jujitsu, and possibly more distant striking skills like Thai Kickboxing. It all depends on your goals though.

I have been studying since the sixties and teaching since 1977. I have found, for myself, that Judo, JuJitsu, Aikido, NinJitsu, Tai Chi, & Wing Chun make a good combined mix ... I get a lot of negative comments like, "Jack of all trades, master of none." But I really do believe the mix has helped me rather than hindered me to reach a master's level. Basically, any martial art with some herbal medicine training to add to the simple "Dit Da Jow" and some more acupressure massage and pressure point target training will make a good enhancement of Wing Chun. Pa Kua (or Bagua) is a much older art that has much of the original foundations that Wing Chun was based on ... they often train inside an octagon of 8 wooden dummies ... Wing Chun, of course is the simplified version in the same way Aikido is a simplified modern art based on the more ancient JuJutsu (both of which would also go well with Wing Chun. Tai Chi & Tai Chi Chuan add a deeper level to the internal controls and meditations and will take you farther in that direction. Any of the harder styles will offer an opposite view point. This may be difficult at first, because it will seem to go against all previous Wing Chun concepts, but will add a whole new dimension. Shotokan Karate or Muay Thai are two come to mind in this category. Any art that has weapons other than just staff and butterfly swords/knives ... Ninjitsu or Budo TaiJutsu or western fencing ... even Zen Archery will help expand your base foundations of ideas, concepts, and strategies ... but when it comes to weapons, other than being good fast weight lifting exercises, you will want to focus your weapon training on weapons that are totally legal, so that you can actually carry and use them ( http://www.canemasters.com/ ). Other than those martial arts and ones like them, other addons may include things that are not actual martial arts but have aspects that are usefull when applied with Wing Chun in a "martial" way ... yoga (and other stretching meditations will help both mind and body), anatomy, physiology, nutrition, history of war and weapon inventions, ALL of the world's religeous books and philosophical books ... will all arm you better with more info, more details, more intelligence, and more wisdom. ... keep your mind even sharper than you keep your sword!

My wing chun sifu studied Brazilian Jujitsu. He said they worked well together.