Here are some Sylvanian Families websites that I have enjoyed:

Official Sites
Sylvanian Families JP - Official Japanese site. Luckily I can still read some hiragana and katakana!
Sylvanian Familiies UK  - Official site of UK. Has a worldwide collector's club!
Sylvanian Families IT - Official site in Italy. Some special European figures available.
Sylvanian Families HK - Hong Kong site showcases both Japanese and UK SF items
Sylvanian Families SG - Official fanclub from Singapore
Malaysian SF Fan Club - Kiki's Sylvanian Page with Fan Club for Malaysia
Calico Critters - Official US site (SF renamed for the US market)
The Sylvanian - SF Themed restaurant in Thailand
Collector Resource and ID sites
These super collectors are a great resource to see past, present, and upcoming SF items.
They also explain rare items and give good collecting tips.

Sylvanian Families.net - Great collectors photos and Wendy also has a custom clothing boutique along with her figure adoption shop.
Jacc's Sylvanian Forest- Great overview and has a wonderful page for rare items called Into the Unknown!

Fan Pages
Here are some websites that have Sylvanian Families enthusiam!
Martika's Sylvanian Families - Go on an adventure with Corntop around the world, even to Grinpa's Sylvanian Village!
Rina's Sylvanian Families - Very cute page and pics
Beverly's CC and Sylvanian Families - Watch a Sylvanian Families village in the making!