Hi Rachel,
What monitor do you have Rachel?
Those with a CRT (Cathode Ray Tube) can be calibrated as there are things that are indeed adjustable. The LCD displays, by contrast, are what they are when they are manufactured and while they may drift from that state as the device ages, the display actually cannot be calibrated. One can alter the brightness, yes that's true, but that is not calibration.
What one does do is to profile the LCD monitor screen output. So various colors are called up by the software then then "puck" one hands over the flat surface, measures that color in hue and intensity and brightness. When all this data is collected, the software creates a table which links the needed color values and the actual colors delivered. 
So from now on to get good color that we want, the software creates a Look-Up Table (stored often in the graphic card, (LUT table) by which whenever a particilar color is called for in an image, the software goes to the LUT and then tells the display to deliver a color as close to the true color as possible.
IOW, every picture is made up of colors that are discovered on a map of redirects! This means that one really needs a great record profile.
It turns out that this is easily done.
A Spyder, even an orginal one used is fine. One can do better but to have a benefit you probably need a better display.
Displays are good or bad based on a number of factors including:
Most displays are attractive and sell well for reasons tha don't help us in photography: Razma-taz bright colorful display for showing movies, playing games and impressing friends.
For us, we need:
A stable display where the profile taken today, will be valid an hour from now or tomorrow and the next week. Often the profle will drift as the electronics and lights age. However, at the very least, the profile should be stable for work in between scheduled re-profiling. 
All LCD monitors need to be re-profiled at regular intervals. 
The display will be most accurate in the center, where it was profiles,  but the profile may not apply as accurately as one works one's way to the edges and corners. 
More money will deliver a monitor that is more atable and uniform over the screen.
If one has a monitor that is at the lower end and drifts more, then getting the most expensive profiling system is not going to necessarily give one better color. the money is better invested in a more sophisitcated screen.
I tried a Dell 23" monitor. This was the birghtest screen I had seen with very punchy color. Unfortunately the color was drifting too much for trusting enough to know whether one needed to color correct a photograph. Buying a more expensive profiling system would be a waste of money.
I have used the Spyder, version ! and it works! It's a colorimeter, very simple but will do the job. If you can afford a better display, then you can still used the spyder, but then the Gretag MacBeth or Xrite spectrophotmeter are worth getting.
Asher