There are 3 types of TI-83 Graphing Calculators:
The original TI-83 (1996), the TI-83 Plus (1999) and the most recent TI-83 Plus Silver Edition(2001).
TI-83 Plus Silver Edition
The TI-83 Plus Silver Edition is best TI-83 calculator: It has the most memory (1.5MB of Flash Memory and 96KB of additional Memory RAM),
the fastest processor and the stand out translucent silver case. It has more preloaded Apps than previous TI-83 calculators.
The best selection and best prices of TI 83 can be found at Amazon.com and Walmart.
At Amazon you have the option of either buying a new TI-83 Calculator or to buy a used/renewed one.
The look and feel of the TI-83 and TI-84 calculators are almost identical. In fact, the TI 84 Plus Silver Edition Graphing Calculator replaced the TI 83 Silver Edition in 2004.
The TI-83 has not been updated since 2001 whereas the TI-84 keeps being updated. The latest TI-84 Edition is the TI-84 Plus CE Python.
Conclusion: Since the TI-83 and TI-84 cost about the same, the latest TI-84 is the better choice. You will enjoy a colorful screen, faster speed, much more battery power.
Additionally, many more preloaded apps and more games are availble.
You may downlad the free TI-83 / TI-83 Plus Manual (PDF) here:
TI 83 Calculator Manual