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 correlation coefficient between women's shoe size and foot length.

Step 1) In order for the graphing calculator to be able to calculate the correlation coefficient. You must change a setting in the calculator. Press "2nd" then "CATALOG" (above the zero button in most TI Calculators) 

Step 2) Scroll down to the "D" area (this catalog list is alphabetical) and stop when you are at "DiaGnosticOn".Press "Enter" 

Step 3) You should see "DiaGnosticOn" displayed on the main calculator screen 

Step 4) Press "enter" 
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 3) Enter the women's shoe size into list 1 and the the foot length into list 2.  
Step 5) Press "Stat" again  
Step 6) Scroll Right to "Calc"  
Step 7) Scroll down to "LinReg"  
Step 8) Press "enter". Your calculator screen should look like the screen shot on the right  
Step 9) Hit "enter" and the last item, 'r' represents the correlation coefficient.  
Your good old TI Graphing Calculator came to the rescue. All of the information that you see in the picture above is quite useful 
r represents the correlation coefficient 