I'll start of by saying I'm lazy and have very few addons. I also forget to open up curse client regularly to check for updates meaning more often than not my add-ons are in need of an update and aren't actually working. It normally takes a couple of days of "a newer version of add-on x is available. update now!" before I update. Writing this has prompted me to check and update my add-ons right now!
Anyway, I do use a select few add-ons including Postal and Auctionator. I find that just using the two to aid my gold-making is sufficient. I love Postal and I'm not sure if I could live without it! It's so simple but incredibly useful. When my bofriend first told me about Auctionator I wasn't really sure how useful it would be for me. Initially, I would even forget to use it and would manually check the AH and work out a decent selling price for an item. But once I started using it I found it to be extremely useful. It speeds up the process of both placing auctions and buying items - which means more time to play!
I'm looking forward to other peoples replies as I'm not even aware of any other add-ons to assist with gold-making.