www.discountdance.com - Take a look at the DANCE SNEAKERS by Bloch.  This is what I wear for my dance classes and I highly recommend them.  They are light, flexible and allow for easy twisting and moving around so there is less impact on the knee.  These types of shoes can also be found at the local dance stores.

www.ryka.com - For Step or "floor" aerobics classes I like the STUDIO shoes at Ryka.  I get the "higher top" for more support for my feet.  You can also get discounts by mentioning that you were referred by your instructor. 

www.youtube.com - Check out videos of some of the line dances I teach by searching “Carrie McNeish”.