There's a good couple that I can think off, off of the top of my head.
Luskwood is on the Mainland, and is a pretty okay spot, and been around since Forever. It's mostly quiet, last I checked in, but still has some good people as visitors. The rating for this one is G.
http://maps.secondlife.com/secondlife/Lusk/216/168/61
FurNation is another one that I remember. The 'Land' is bigger than Luskwood's, but that includes the fact they have 3 sims, too. The rating for this one is M for 2 of their sims, with the third being A.
No link for the Browser map because it's too wonky for me. If you look for it in the viewer's map, FurNation Phoenix is their main sim.
Unfortunately, these are the only places I know for certain that is still active. By that I mean 'Around after 5-6 years.'