Have a look at this site:
http://inmykit.com/. It is stacked with great products to have in your kit and why. Obviously this is one (fantastic) MUAs opinion but it's been my go-to list while I've been stocking mine.
Also do a google for what MUAs stock in their kit. I found a great resource once where everyone listed what they had in their kit and some of it was very surprising but very helpful as it was stuff I hadn't even thought of.
Personally, at the moment, I have a mix of MAC, Face Atelier and Yaby for foundations and I'm about to buy some MUFE HD foundation (very popular!) to add to it. Yaby do fantastic eyeshadows, and I have some MAC eyeshadows too.
If you want to have some more MAC have you thought about going to your closest MAC and just having a chat with them about what you are looking for? eg: what type of foundations etc. I did this once and it was a great help.