TI MathForward is a solid way to use graphing calculators in block schedules. Also, the latest revision to TI-84 software allows pretty print display. All TI-84's should be upgraded.
The TI NSpire has been upgraded. Each teacher can send only one to TI to be swapped with a new one by Dec 31, 2010. IMHO, the nine (ten) or more NSpires at Estancia should be sent to TI, one at a time, with a different teachers name; so that the whole small set can be upgraded. Other schools should act similarly.
HP doesn't make new calculators anymore. The division was sold off to a reseller.
Low Cost Classroom Sets
The Sharp EL-W535 ($10) and EL-W516 ($13) deliver the natural display features of the Casio fx-300ES (HP 300s) and Casio fx-115ES, respectively at lower prices with, most importantly, faster input/output of fractions. However, initially the Casio is chosen by students because it's display is the most natural. After showing the faster Sharp output, they switch. The Casio fx-300ES does have a list feature, that the EL-535 doesn't and it's battery may last longer because of a solar panel for power. With the list feature, the W516 can serve a student from Middle School through Statistics. TI's two line calculators aren't as fast or useful sadly.
Only AP Calc and AP Stats require facility with a graphing calculator.
In short, the Sharp W535 would serve well for class sets in middle school. In high school, the 516 would work. These calculators can be used in a variety of STEM classes, where students would/could understand how to use them. Letting everyone use different calculators is similar, but not as big a problem, as letting everyone use a different text. The current standard practice of anything goes with calculators is and has been incorrect.