This is a list of SIOC-enabled sites. This list is also available in RDF here and mentions SIOC data URL.
Take a look around the world - Sergey Lukichev's travel blog
AI3:::Adaptive Information - Mike Bergman's blog
Dobrometr (RU) - similar GetThingsDone service
journals.ie - A Wordpress Multiuser site, all the blogs are SIOC enabled
B:\datenbrei - Wordpress2.0, mixed language content
#B7erge - Wordpress1.5, all german content
Alexandre Passant - Personal weblog using Dotclear exporter
Infopirat - Drupal based news and blog site, SIOC enabled
NoticIEEEro - A WordPress site sharing articles and announcements about IEEE Region 9, Latin America and the Caribbean, mainly in Spanish. The blog is SIOC enabled.
Needle Blog - A WordPress site for sharing news from the Needle (semantic digital libraries) community
Casual.info.in.a.bottle - Personal blog in italian and english about Web and Semantic Web
Weblog Data Space - Kingsley Idehen's Blog
OpenLink Virtuoso Tutorials Data Space - collection of Virtuoso tutorials covering SQL, XML, RDF, and Web Services
The Blog of Athos - by Juan Miguel Gomez
randgaenge.net - a blog on Social Software
Bamblog - by Jan Schmidt, in german
http://torrez.us/ - by Elias Torres
The Hundredth Monkey Phenomenon - by Rob Gonzalez
Operation:Teleport - did you ever want to be someone else?
La Comunidad de AsturLiNUX - AsturLiNUX blog community
Augmented Cognition Blog - AugCog from a garage perspective
Innovative SEO Tools - RELAX SEO Services - Innovative Tools and Training
semwebdev Keith Alexander's blog.
Future Trends - a ThirdForce R&D blog
contentfree.de - Rolf Strathewerd's blog, german content
www.aetherworld.org - Alexander Graf's blog
To detect the presence of SIOC RDF data on web pages you may use Semantic Radar - it is a Mozilla/Firefox extension that detects links to SIOC, FOAF and genric RDF and RDFa data (via auto-discovery information) and displays status bar icons. Clicking on an icon will allow you to browse the corresponding RDF data.
If you are not using Firefox, you may use the SIOC Browser directly.