Here's a link to the AAVSO bulletin which has predicted maxima and minima for Long Period Variables.
http://www.aavso.org/publications/bulletin/
Read the instructions on how to use the bulletin. Unfortunately the latest bulletin covers to the end of 2005 only. You could add 332 days to the last maximum.
Here is an article about Mira which has maxima predictions but, again, stops at April 2005!
http://www.seds.org/~spider/spider/Vars/mira.html