There are a lot of good model train blogs:

Needles Division Santa Fe RR N Scale: http://needlesdivisionsantaferrnscale.blogspot.com/
Santa Fe Railway Southern Division: http://santafesd40.blogspot.com/
N Scale Union Pacific Railroad - Class I Midwest Model Railroading: http://genevasub.blogspot.com/
Model:160: http://www.model160.com/
O Scale Trains Magazine Online: http://oscalemag.com/wordpress/blog-home/
Eric's O-Scale Railroading Journal: http://ericstrains.com/journal/
David's O Scale Blog: http://davejfr0.blogspot.com/
CTA O Scale L Layout: http://ctalayout.blogspot.com/
Zetts EJ&E Layout: http://zettsoscaletrainlayout.blogspot.com/
2-Rail O Scale Railroading: http://2railoscale.blogspot.com/
Modeling Insull's Empire in O Scale: http://modelinginsullsempire.blogspot.com/
Lionel Blog: http://lionelllc.wordpress.com/

As far as platforms, you can go with either Wordpress or Blogspot. What sort of material would you be placing on the blog?
SFF3