Graphs and Transformations take center stage in Algebra II. We spend most of the year discussing the major parent functions, looking at their graphs and noticing how parameter changes would affect that graph. Studying these pictures with a TI is a very low-res experience. They have activities available on their website that involve lots of button pushing and hand holding. I have found that better results are obtained when you can dynamically show the effects of a parameter change. There are some nice modules through Explore Learning that I have used (the conics ones are quite handy). The only problem I have with those is you get 5 minutes to play with a particular module per browser per day. You can sign up for a 30-day trial but the only other option is to get a site license for your school. Using them as inspiration, I stumbled upon Mathematica, a way overpowered tool that has a great feature that lets you build interactive models. I was able to crank out a few in not a lot of time:
The lag in the sliders is from the screen capture delay, the modules are quite responsive in practice. I have embedded the actual modules in my Algebra II and Pre-Cal curriculum sections. You can also download the CDF files and play with them offline. In both cases you'll need Wolfram's CDF player/plug-in (it's free). Have I mentioned that my curriculum sections are fully loaded now? Go look.
I'm still trying to fiddle with modules for conic sections, but plotting implicit equations is a little trickier, plus there's a giant CDF repository where others have come before me and accomplished good enough results.