I would have thought Voice Search. I find it interesting that you think excluding the Text To Speech process would help - that's only used for converting text to speech, not speech to text.
This kind of thing is exactly why these task killers are bad. Most people who use them don't have a clue how they work, what the side effects are, or how Android handles processes.
Basically, people want to kill tasks to make things faster and free up some memory. Well... in most cases they're killing off processes that will just have to restart (this wasting the processor power killing it, wasting the processor power freeing up the used memory, and wasting a lot of processor power loading it back up again). Meanwhile, after it loads, it will be using more memory than it was when you killed it, because memory that is used but not needed often is often compressed into the comp-cache. End result is that you end up using more memory and a ton more CPU.
It's also worth noting that Android will remove processes automatically when it gets low on memory - there's no need to do it yourself or have an app to do it all the time.
Services running in the background, unlike in Windows, really do use 0% CPU on Android, unless they're actually acting on something.
My advice would be to exclude EVERYTHING from your task killer, unless you're 100% certain it's something you don't want running ever. Remember though, that apps leverage code in other apps, for example it's common for people to think it sensible to kill off the Calendar service if they don't use the Calender, but apps sometimes use methods in the Calendar to schedule events (alarms, updating stuff, anything that happens every X minutes or at a certain time). So killing the Calendar just means it has to reload a few minutes later.
