Here's my list of friends, sites you should check out for help or activities, and my favorite content creators.
Help and Activities
Builders - A community on Livejournal for practicing your lot
building skills. Anyone can build a nice house, you just need to
Pixel Trade - Simmers sharing sims. To give a twist on the popular legacy challenge, you use a founder made by someone else, then marry in sims shared by others.
Sim Mania - Quick, one round contests. Tired of contests where the hosts or judges go MIA? Try Sim Mania
Simply Home - A lot decorating challenge community. Challenges can be from decorating one room, to decorating a themed restaurant.
WCIF sims - A Livejournal community dedicated to helping simmers find desired custom content. We also do weekly themed finds lists.
Wella Creations - A Livejournal community for advertising most types of creations.
Black Pearl Sims aka Forum Formerly Known as Reflex Sims Forum - If you're looking for a forum that doesn't only have the same old modeling contests, check out this one. They have decorating and building contests, as well as member run ones and a recoloring contest.
- Great handpainted clothing
All About Style - Great clothing in a variety of ages and themes
Around the Sims 2 - Sandy is a consistently high quality object creator, since Sims 1
Holy Simoly - Great sets of furniture that coordinate and in a wide range of colors
Lord Darcy @ MATY - Some of the best fixes out there. His more slots for Maxis furniture are essential.
Raonjena - One of my favorite hair creators. Their orange shade is my pick for my own hair color
Rensims - Great hand painted bodyshop content
Rosesims - Another of my favorite hair creators
Simbology - Twojeffs is an awesome hacker
Simlogical - Inge is still making her awesome hacks. Also check out her stairs.