The only real way to 'stop' or remove these unwanted apps is to root your device. Not necessarily ideal for every user out there, but most of these unwanted apps are 'bloatware' placed on the device by carriers/partners and sometimes manufacturers. For the most part, no one likes this stuff... but they keep putting it there.
With root access you can simply rename the .apk's for these apps to .bak and they will essentially be hidden from the OS. Flat out removing apps isn't recommended unless you're comfortable with the in's and out's of rooting/ROMing/SBFing etc.
Using a task killer to 'kill' them as they open is only going to be more resource intensive on your device as these programs will continue to open, because it is how the OS is designed to operate.