Im looking to lower my 2000 s70 glt, but should I just replace the shocks or redo the whole suspension? Also, who makes the best suspension/shocks?

Most people will say save the money and redo the whole suspension at once.

I agree, but you don't have to.

http://www.shox.com
http://www.ipdusa.com
http://www.eurosporttuning.com
http://www.vivaperformance.com

Check these sites out.

-Lowering springs
-Shocks/Struts
-Ipd sway bars

Those three mods will do you very well.