Before we discuss the latest strategies to deal with this you might want to look at your analytics. Sometimes Google's dynamically generated title tags actually boost CTR and deliver higher traffic for a site.
I find the first step in dealing with it (assuming it even needs to be dealt with) is to make sure all pages have significant & relevant title tags. I find many sites have anemic or identical title tags. Then make sure your internal linking is properly setup with good anchor text.
Here is a checklist to help people trying to deal with their page titles being changed.
#1 - Are you losing or gaining traffic? It is quite possible that Google is displaying a title tag that generates more click-throughs than your original one. If there is no change or an increase in traffic I would not spend time on this. Personally I would leave my ego at the door and let Google do what they do while I optimize other areas of my site.
#2 - Is it pulling from DMOZ or Yahoo Directory? If so add the appropriate meta tag.
#3 - Log into Google Webmaster Central. Pay attention to the link data & the analysis of your site's content.
#4 - Is the title tag in the serps being dynamically generated? Is it pulling from text on the page? If it is pulling from text on the page you might want to tweak the text that is being pulled. Caution - tweaking page content can impact your rankings.
#5 - Is the title tag being generated by your anchor text? There might some ROS link(s) influencing it. You can try to tweak the existing anchor text or develop new anchor text. Caution - tweaking anchor text can significantly impact rankings.
#6 - Make sure you are not chasing a temporary Google test. Google runs hundreds of short term tests every year. It is generally not wise to invest too much time & resources on a temporary test that will revert back to normal in a few days.
#7 - Is this part of Google's personalization campaign? Test to see if others see this or if there is a certain trigger (past searches, time of day, etc.)
Keep working and trying new things. Google is not simple and grows more complicated everyday. There is no short checklist that could thoroughly cover Google's current & future handling of page titles. Good luck!
goodroi -- Your suggestions for how Google might generate these altered titles are logical and sensible. But most of the titles that Google generates for pages on my sites are not logical or sensible. That makes it almost impossible to find a remedy.