I have been asked variants of this question quite a few times in the last few weeks so I thought I would address it. Last year we described how to wipe all the information off your BlackBerry through the OS. The problem a few people ran into is that sometimes this is not exactly possible. For example, Phil ran into a situation where he wanted to wipe his BlackBerry but his keyboard was broken.
The simple solution to this problem is to use Javaloader or JL_Cmder to wipe your BlackBerry through your computer. You just need to plug in your BlackBerry and install the free JL_Cmder application from Doug at BBForums. You then run the application and select the #4 option which will wipe your BlackBerry. You can read more about using JL_Cmder in Nate’s review.
Let us know if you found any other ways to get this done!