If your preferred spelling is 'blogoversary', you can go to this site and register your blog. They will generate the code for you to put a button on your sidebar for quick blogoversary reference. It appears to be free. They will also feature your blog on your blogoversary. I didn't sign up.
'Bloggoversary'? Google asks if you meant 'blogoversary'. See above.
If you Google 'bloggiversary', Google thinks you meant one less 'g'. See below.
'Blogiversary' will lead you to the Urban Dictionary definition. It was added in 2005. Strong provenance.
'Blogaversary' and 'bloggaversary' do not yield anything of interest to me.
I'm going with 'blogiversary'. Happy Blogiversary to me.
My first post was completely uninspiring. A year hasn't changed much.