Consolodating Categories

At our wordpress site, http://thefullpint.com , our category tree is getting out of control in length.

I would love help in figuring out the best way to consolidate cats or having a plugin that would allow me to make parent cats, having the user click it, and then the sub cats expand in a ajax like manner.

When I say consolidate, my example would be consolidating American Double Stout, Russian Imperial Stout, English Stout into one category called Stout.

I would much like to not have to go through each and every post to do this.

Thanks in advance for any help.