Im getting 4 16" steelies for the winter, now I need some rubber. What size should I get to keep the speedometer accurate?

 

What do you have, the G6 wheels? Try the 205-60R16 which should be closer than the 215-55R16 tires that were stock on them.

 

Try using this...

http://www.s-series.org/htm/calc/tiresizeconv.htm

First put in the your summer tire size, record the diameter... then keep putting in potential winter tire sizes until you find the closest match...

I did a quick calculation... the stock SS/SC tires (215/45R18) are 25.6" diameter...
The 205/60R16 are 25.7"
The 215/55R16 are 25.3"
So, go with what css9450 said; the 205/60R16.

 

discounttire.com has a pretty good conversion tool buried somewhere too

 

Here is a really good conversion tool that shows how far off your speedometer will be with different tire sizes.
http://www.wildweasel.ca/j-body/HowTo/tirecalc.asp

 

I put 225/55R16 on mine and I have only had one of the tires rub once when backing into a parking space.
Stock 215/45R18 is 25.6"
225/55R16 is 25.7"