All modern TI graphing calculators (that I know about) allow you to calculate various types of statistics. The TI84 Plus, in particular, has a powerful suite of statistics tools. 
Demonstration problem: Calculate the standard deviation of the following set of data { 50, 20, 33, 40, 55 } 
Step 1) Press "Stat" 

Step 2) Hit "enter" button and you should see the three lists on the right. In the next step we will enter all of the scores into L1 

Step 4) Press "50" then "enter"  
Step 5) Enter the rest of the data into the calculator by pressing each of the numbers then 'enter' :20, 33, 40, 55  
Step 6) Return to the main calculator screen by pressing "2nd" then "quit"  
Step 7) Press "Stat"  
Step 8) Scroll right to highlight "Calc"  
Step 9) Hit "enter"  
Step 10) hit "2nd" then "L1"  
Step 11) Press "enter 
Your goold old TI Graphing Calculator came to the rescue. All of the information that you see inthe picture above is qutie useful 
X represents the arithmetic mean 
represents the standard deviation 
Therefore, this set of data has a mean of 39.6 and a standard deviation of 12.4 