I've mentioned some of these elsewhere - these are things I'd like to see built for my 8110 now & for my 9000 (on the waiting list) ASAP:
EMBEDDED-BATTERY HOLSTER WITH CLIP. I want a slender battery & some pass-through charging connectors built into the back (the part that snugs against the BB battery door) of a slim holster with swivel clip, and I don't want the clip to block any of the back-panel or side-panel features.
MULTI-OUTLET STEREO HANDS-FREE BLUETOOTH CAR KIT. With more states mandating hands-free operation, it makes sense to build a car kit that can handle a lot of the things a BB is good at, from stereo media player (through its own speakers or an FM radio retransmitter) to noise-canceling mike and maybe one variation with a built-in GPS puck on a second BT channel. More important: when it plugs into the lighter for power (note: it should have its own built-in rechargeable battery to keep running when the lighter plug won't work with the car off) it should pass along at least 2 USB connections so I can still use the car to power the BB & a BT headset (for when out of the car).
CAR DOCK WITH SECRET WEAPONS. It helps to hold the BlackBerry up where you can see the screen (as when using a navigation application) and a dock that just does that is pretty cool, but it's cheap & easy to add to that. Configure it with a USB mini-5 to slide into a BB model's connector to let the handset run & charge. Build a patch antenna into the back that comes out to a standard RF connection (something like a Wilson dock) so a signal booster doesn't have to add a piece. Include a place to slide in a mating Bluetooth GPS puck accessory for handsets that don't have GPS built in. Include an additonal USB connector at the bottom & hook on the back for charging a headset. Let it run from a lighter plug that also offers additional USB-A power ports, plus a LED to confirm the lighter plug has power. Give it a small adjustable shade on the top to help fight sun glare.
SMART DESK DOCK. Include a jack in the back & a patch antenna next to the phone plus a small WiFi booster inside. Include a small float-charged battery inside so the phone can get fast-charge current even if the USB port isn't delivering it & to keep it working during outages. Include secondary USB-A charging ports for a BT headset & whatever. Give the bottom one of those slide-proof/mark-proof rubber pads. Include a sensor to light a LED if it senses the phone vibrating; keep that on (in case you weren't there at the time) until the user resets it. Do not put a clock on it or in it. If there's room, include a side pocket for a micro fiber cloth for cleaning the screen.