What is the best way to stack up wedding cakes? I have only tried the dowl rods in the middle and that dosent seem to work to well? Any ideas???

If you're only placing a dowel rod down the middle, that's not enough. That won't support the tier above it, it will only keep the tiers from sliding. You have to support the tiers above each other by placing dowels on each tier except the top one of course.

I use bubble tea straws and I love them. They are really easy to cut and they support well.

However I'm going to be doing my first wedding cake in Oct. and I am going to look into using SPS since a wedding cake is such a big deal. There's lots of information about SPS on CC.

Here's one way:
http://www.wilton.com/cakes/tiered-cakes/stacked-tiered-cake-construction.cfm