Update: There is a Motion Lab/activity that can serve as a nice introduction to the CBR2 available at this link.
This is an exciting time. I would say that with the use of the TI-Nspire Lab Cradle the number of probes/sensors that can be used nearly doubles. According to a Vernier website the number of available sensors if you are using the Easy Link or Go Link are 50 and with the Lab Cradle it is 58. However, let's say you have some old sensors in the stock room that you thought you would never get to use again. With the right adapter, I have now tested an old accelerometer, pressure sensor, a microphone that was designed for the CBL, and just today I received the Motion Detector Cable MDC-BTD and got the original CBR to collect data as shown in the picture. (Thanks Grant, a top AP calc & physics student, for having your camera and taking the pic.) So the $145 TI-Nspire Lab Cradle can be a really good deal if you have some older equipment. Potentially hundreds of dollars of resources can now be used again and you won't need the approximately $60 Easy Link.
[Update: I've used the Easy Link with the older equipment with great success. Note that there are several data collection sensors like the microphone, photogates, and motion that will not work with the EasyLink's one 'BTA' port, but need the Lab Cradle's 'BTD' ports. The Lab Cradle also has 3 places to plug in 'BTA' plugs so you can, for example, measure temperature of 3 things at the same time like we've done with this evaporation lab.]
Now to the question about 'what data collection equipment should you get?'
If I was consulting your school and helping you develop a plan that fit your teachers, I would begin by asking several questions. But since we aren't having that dialogue, I'll give a general response.
If you don't have any sensors, and you have less than $150, the two data collection probes that all schools ought to have for science and mathematics would be the temperature probe and motion detector - Easy Temp and CBR2.
Neither of these require an additional interface. You can plug them directly into the mini USB on the top of the TI-Nspire. Similarly, if you have have a $5 mini to standard USB adapter, then you can plug a Easy Temp ($38) or CBR2 ($93) into your computer and the Nspire software will auto-detect and begin collecting data.
The gas pressure sensor is another one that (along with Easy Temp) is especially useful in bio, chem & physics.
I was recently asked what sensors I would recommend for an environmental class. Take a look at the recommended probes with the lab book "Investigating Environmental Science through Inquiry." Instruction are provided for pH, conductivity, soil moisture, O2, UV sensor (this appeals to many classes), light sensor (I bet you have that one from your CBL days), etc.
Most of these work with the Easy Link. But you cannot use the microphone with the Easy Link.
That is why I'm so excited about the Lab Cradle: multiple probes, extended battery life and help to power probes with the built in rechargeable battery, AND more sensors that I have been wanting to use.
I think math and physics teachers will be especially excited by the microphone. With a tuning fork you get real-world sinusoidal data that gives audible significance to the general equation y=A*sin(B*x)+C, where B=2pi*frequency or 2pi/T, the period. In mathematics they tend to call the coefficient in front of the x-variable B, but especially when dealing with rotational motion, like a Ferris wheel, I prefer to call it omega, the angular velocity. We used a 512 Hz tuning fork to get the data shown in the screen capture. The curve fit gave a value of 511.7 Hz. I love it!
[Update: Microphone lab with the TI-Nspire and many more are now available from Vernier.]
In addition to the microphone, with the Lab Cradle the 3-axis accelerometer, photogate, nuclear radiation monitor, and rotary motion sensors are new comers to the Nspire family that will be useful for mathematics and science classes.