Are there any reasonable complete open-source C# .NET blogging engines out there? Something a budding programmer may be able to extend? MVC Ideally.
BlogEngine.NET is great. Easy to create your own extentions.
Subtext and dasBlog is also worth a look. Current version is not MVC, but I've heard the future versions will be MVC.
Oxite is built in MVC, but it's been getting bad reviews.
See more here, http://stackoverflow.com/questions/180800/any-free-or-commercial-blogging-engine-recommendations
You could look at DasBlog. I'm not sure if it's MVC based but it's maintained by several famous Microsoft guys. And I seem to remember something about it not requiring a database.
BlogEngine is something good but it has some limitations comparing to a great blog engine such as WordPress.
Also i heard that Graffiti is very good.
I am using WordPress and Blogs inside CommunityServer
I havent personaly used it but as you said you wanted a MVC based blogging engine you could try Atomsite.
The plus sides as I see it is that the admin interface look very much like wordpress, but as I said I havent personaly used it just heard about it.
For more of a full MVC CMS I can recomend N2