Hey, I only have a TI 84+ (non-SE), and I am taking AP Calculus.
I have noticed already when using the calculator in class that I can't do everything because the TI-89 titanium (which everybody else has) has better software.
My teacher also recommends to get a TI-89, and I'm wondering, should I get a new calculator for the AP test I'll be taking (AP Calculus AB and BC), and if yes, should it be a 89? Or is a nspire cx the better choise then?
Please help me

I have trouble with a lot of stuff, like derivative function (of cource by hand is possible but sometimes you just wanne use a calc), solving indefenite integral (again, same as derivative), factor, expand, sec, csc, cot (it sucks always doing 7/sin etc and i'm not using symbolic anymore as it doesn't play so nice with graph3), then also these functions (I forgot the name) where you draw the real funciton out of the derivatives (graph3 doesn't has so many options on it as the 89) and I bet there is more.

I'm biased toward the nspire.
Get an nspire

Does the OS itself of the nspire have /all/ the maths features the 89 has?

EDIT: I just saw here a list of calculatores allowed in the policy for the ap test (BC) http://www.collegeboard.com/student/testing/ap/calculus_bc/calc.html
And it says that the ti-84 has everything they recommend on software stuff, but I've been missing these other features mentioned above in class so i'm wondering now if i need a new calc at all.....

If your teacher and peers use the 89, i would recommend you getting it too, for simplicity.

It may be useful to have it, but I would avise a CX CAS if it's allowed on the test if you choose to get one. I personally use my prizm in class. It does everything I need it to do. You can do numerical integration and I know symbolic well enough to do it quick on my own.

I would get one.  Although you can do many things by hand, the AP test is timed and a calculator with a CAS will save you time.

Get an Nspire Clickpad (blue one) used, you can use it on any test you can use an 84 on, and you can also install the CAS OS using Nleash when you aren't taking a test so you have that.