I have long liked WordComplete (Word Complete) from CIC, but CIC is long gone and the app is not really compatible with the Tungsten E2 OS and wretched nonvolatile RAM.
Today I found there is a potential replacement: TextPlus by SmartCell Technology. I'll give it a try. $20 to register, 30 day trial. That's fair.
Update 3/13/06: Wow, that was a quick trial. Here are the uninstall directions. TextPlus is complex, big, and utterly incompatible with TealMaster, TealScript, & TealLaunch. Those apps are far more important to me than TextPlus. I'll switch back to the old incompatible WordComplete. It is only slightly crashy.