There are many different environments that can be used to develop calculator programs using z80 assembly. Here are a few more options.
Brass is an assembler targeted at the TI-83+ by Benjamin Ryves. It can be found on his blog, Ben Ryves Blog
Zilog Developer StudioEdit
ZDS is the official IDE from Zilog for working with their processors. You need to do some work to get an enviornment, but it is fully featured. It is known to be used by Drew DeVault and Brandon Wilson in the community.
Some people enjoy programming directly on their calculators. This is not as easy, or as supported as elsewhere, but it is possible. One option is to learn to code in pure hex, and use TIOS to compile it. Another option is OTBP Assembler, which can be found at TI-Calc. An on-calc IDE called Mosaic is in development as well.
Setting Up Your EnvironmentEdit
Setting up to develop for the TI-83+ in assembly can be a daunting task. However, there is almost always someone willing to help. You can find help at #ti on IRC (efnet) or at one of the various calculator forums.