Every fan that I've replaced has been a 120mm fan with two (or three) wires, that only needed two wires to run. For the most part, if it comes with a plug, I'd cut that off (because it didn't fit) and solder the reds and blacks together. I've used all qualities (prices) of fans and it seems that they all eventually fail. I've even gone to Best Buy when I was in a jam and purchased from them as well. Recently I order a multipack....typically four of five fans, from eBay for 10-15 bucks. They most likely are coming from China, so it takes a month or so to arrive. I always have extra fans ready to go.
EDIT TO ADD:
The link for the fans I last bought is no longer there. However, I did find this three pack of fans for ten buck....and they're located here in the States. Just make sure you have 120 by 25 mm fans that have two wires....typically one red and the other black.