Hey there! My name is Sam (though it's been Lufferkinz and then Lufferkinzify since Sims 3's release in 2009), and I'm an avid Sims lover like you, but I really love The Sims 2 - it's been my favorite Sims game since I was very young. Well after The Sims 3's release I haven't been able to play it until about 2 years ago when EA released Sims 2 Ultimate Collection on Origin for free, and by that time the community was dying and a lot of custom content resources that I loved were dying away or hard to find. So I figured I would compile this list to help others find CC as The Sims 2 is basically unplayable for me without it!
For those new to Sims 2 custom content, here is a basic guide on how to mod your game. (I recommend using 7-Zip instead of WinRar as your extraction program, though. 7-Zip is free)
Be sure to use Clean Installer whenever installing sims or lots you know contain CC.
Also, since this is a T rated forum, all download links listed here are as well.
Now, onto the list!!
Sims 2 Graveyard
This site is a blessing! If you played The Sims 2 long ago and played with custom content, chances are your favorite creators and their sites have poofed off the face of the earth. This is where Sims 2 Graveyard comes in, people share the creations of 'dead' creators and links and list them on this site for all to enjoy even though the original source is forever lost. So if you recall a past CC creator you loved, but their site is now gone, it's worth a shot since everything is categorized by creator!
ModTheSims is a big favorite of mine and are mostly good for game mods but some of their other downloads are pretty amazing too! The community is awesome as well making for tons of unique downloads.
Garden of Shadows is my FAVORITE place for alternative style (and other) beautiful CC. I've linked the main forum for Sims 2 downloads but they also have downloads for TS3&4. Like ModTheSims, it is community driven so you get a lot of unique download options.
Tumblr or Simblr blogs are amazing sources for CC. Some of my favorite creators include Lillith Sims, Azaya and Anitka Sims. There are also 'CC finds' blogs such as TrappingCrushes (although no longer active), and Lana CC Finds. You can also get a lot of luck simply by searching on tumblr sims 2 cc or sims 2 clothing/hair/makeup/lots etc
Mouseyblue has a ton of high quality CAS/bodyshop downloads!
FemmeFatale is really good for 'hipster' female adult clothing!
LianaSims2 has tons of fashion downloads. I am not of a fan of their clothing, they are too photoskinned or unrealistic looking for me, but their accessories and nails are gorgeous!
CoolSims has been around for soooo long and they're known for their hairs which are popular to recolor/texture. Some links are broken but their downloads are great!
XM Sims has tons of stuff. Especially fantasy stuff. It's on the older side so some of their stuff is outdated but some of it's worth a look.
ButterflySims is also popular for hairs and a lot of people like to retexture and color them. Keep in mind quite a few of their downloads are donation only but you can easily filter the hairs that are free on the left side (under Sims 2)
My Sims 2 Blog is an awesome Sims 2 CC lister!
Paranoid Illusions makes beautiful furnished homes
This list is constantly being updated so if you have any requests for a category or a website recommendation let me know and I'll add it to the list
Last but not least, if you are looking for something specific and Google yields no luck - try asking in the Sims 2 WCIF forum on ModtheSims. Annndddd I hope I helped someone!!

So I wanted to do a post about some safe custom content web sites. Since people are always looking for them. If you have a website that is safe and has quality CC then post the link and I'll put in here!
http://anubis360.blogspot.com/
http://www.thesimsresource.com/ (be sure to have an ad-blocker on this one)
http://www.lorandiasims3.com/index.php
http://modthesims.info/ (you need to register to download)
http://www.beocreations.com/ (you need to register to download)
http://lianasims3.net/index.php
http://mysims3blog.blogspot.com/
http://khaleesi-cc.tumblr.com/
http://lapizrazuli.blogspot.com/
http://m1ssduo.tumblr.com/
http://liahxcc.tumblr.com/
http://www.aroundthesims3.com/index.html
http://eternila.tumblr.com/
http://www.spring4sims.com/
http://www.parsimonious.org/furniture3/pages/all_1.html
http://masims3.blogspot.cz/
http://lovesims3stuff.blogspot.com/search/label/Accessories
http://beaverhausenx.tumblr.com/
http://www.freshprincecreations.com/
http://julianascorner.blogspot.com/
http://sclub.mktm.co.uk/en/
Hope this helps!