If you plan on getting a lot of cc or using a lot of mods, I highly recommend Raxdiam's Mod Manager for package files. While I second the recommendation to use 7-zip (frankly a lot of modders use 7-zip to compress, extract, and manage files they're working with in the first place), if you're only using cc and .package files then Mod Manager will automatically extract those files (it does not work however for the new ts4script files so you would still have to extract and put those into your mods folder manually).
As far as sites for finding cc, both
thesimsresource.com and
modthesims.info (where you can find the formerly mentioned Mod Manager) are still good places to start looking, along with the other suggestions here. A lot of times if you find a particular cc-creator whose work you like on larger resource sites you can google their username to find them on tumblr, wordpress, etc., where you can see more of what they have to offer. Tumblr itself is a pretty big go-to area for cc creators, so you may even try just searching for a few keywords there and see what you can find going down the rabbit-hole (same with Pinterest).
