There are dozens of sites with custom content for The Sims 2. Be sure that you read the tutorials on how to install custom content. I recommend The Sims 2 Wiki:

http://www.sims2wiki.info/wiki.php?title=Main_Page

Read the articles about custom content. Save yourself the headache later and organize what you download into folders so you can find and remove it later if you get tired of it.

Some of the sites will require that you register, for free. Some call themselves ‘Donation’ sites. Since by definition, donations are optional, when you encounter such a site, go instead to The Booty:

http://paysites.mustbedestroyed.org/booty/

..and download pay/donation content for free. No registration required.

The booty is organized by Site name, then by artist name.

Sites that I have custom content from:
http://www.modthesims2.com/
http://elitesimbuilders.com/
http://illustratedsim.tripod.com/
http://isleofmaltha.com/
http://moonsims.asi.org/dh-sims-site/sims2index.html
http://n99forumpaks.djssims.com
http://noukiesims2.net/wp/
http://simsfashionbarn.net/SMF/index.php
http://sunairsims.enorth.com.cn/chou/images/credit.htm
http://www.aussietopenders-sims2.com/Gardening.htm
http://www.holysimoly.com/
http://www.modthesims2.com/creator/marvine
http://www.notovny.com/misc/index.html
http://www.parsimonious.org/links/links.shtml
http://www.peggyzone.com/
http://www.piggis-sims.net/index.html
http://www.simfantastic2.com/packs.htm
http://www.simslice.com/thesims2/ts2objects-pg3.htm
http://www.thesimsresource.com/artists/Cyclonesue/

The best hair is from
http://www.xmsims.com/
http://www.peggyzone.com/
http://www.raonsims.com/main/main.php
http://hideki.modthesims2.com/download.php?f=342&u=23182

If you create custom items using someone else’s content, they will require that you adhere to some reasonable rules, like don’t upload to the EA Exchange or to any paysites.