To allow commenting on blog posts I decided to use the extarnal service Disqus. This has some advantages like, no serverside logic implemetation for handling comments on my side ;], but also it prevents spam to some extend and it provides some social features, like suggestions for other blogs with related content.
The disadavtage is of course, that you have to sign up for yet another Web2.0 account. But you can re-use this account for any website using Disqus. An other con is, that it is not possible to post anonymously, but I would most probably not allow this even if I implemented some blog post commenting functionality myself...
I am happy about any feedback to my posts, so start spamming my site (and lets see how useful Disqus spam prevention is :D).