I've been a big fan of Kevin Daly's blogging app for Windows Mobile devices for quite a long time now. But until I recently got a Blackjack, I had only used it on a Pocket PC. Well Kevin kindly responded to my begging and updated Diarist for smartphones! You can download it from the Channel9 sandbox at https://channel9.msdn.com/showpost.aspx?postid=302954.
I can vouch that it's quite capable and works great. In fact, I used it to write and publist this post!
For Pocket PC users, get the latest version of Diarist at Kevin's website.