Here are some of my favorites for my BOLD - with links on where to purchase them from Seidio
Links are too specific pages but look around for more options and combo deals.
Bluetooth - for the car I use a Blueant Supertooth, and for talking inside I use a Jabra BT-530.
Other must have needs are the following items.
For the 9000, its a 3500 mAH.
An extra battery is essential if you have a 3G unit like a Bold, and a multi-unit charger that you can use with various cell phone battteries is ideal. For my old curve I had a super extended battery that I used on weekends when GPS use was heavy. The extended battery for the bold is reviewed here.
For cases, I always have a high-quality swivel belt-clip and a sleeve case. With some swivel clips you can have rubberized sleeve cover and use the belt-clip too. You can buy these in a combo deal too.
Seidio has a new line of case, called the Snap which are easy on, and easy off. I LOVE the SNAP line of cases for everyday use to add a better grip to my 9700 and give it a little protection if I drop it.
No matter where you go you should have a screen protector. I am also fond of those sold by ScreenPatronus.