Without a doubt - 100% willing to pay big bucks for - I WANT TO BE ABLE TO RECORD MY PHONE CALLS DIRECTLY ON MY PHONE!
Right now I hook up a whole bunch of cables and use a wired headset or I hold my digital recoder up to the speakerphone - stupid when I can record on a Treo without any problems.
I'll pay $100 for a phone call recorder. That market is 100% unserved in the Blackberry community.
If we must pick from the choices on your web page...
Show traffic report on the home screen background image
I wouldn't mind a traffic report for a specific route as a home screen background image. You could define multiple routes such as home->work and work->home routes at specific times each day.
Before I drive to work in the morning, I would like to quickly glance at my BB's homescreen to see if there are any traffic incidents along my route to work; if there are any incidents, I would be able to press a key to see an alternative route. Similarly, at the end of the day, I could check my Blackberry to see if there are any incidents from work to home.
These incident reports would be displayed automatically for the appropriate route based on the preset times for that route (i.e. M-F @ 6:30m: home->work; M-F @ 5:30pm: work->home). The ability to see these alerts on the home screen with a glance is key. I am not going to spend five minutes to open and check a program to see if there is traffic along my route.
Automatically forward calls to a land line next to you
If you are going to do this, make sure you include a scheduler so I can automatically forward calls based on day/time. Sprint charges $0.20 per minute for forwarded calls, so you might look into supporting some alternative means of call forwarding.