I was wondering if there is a certain kind of royal icing that i can buy from the store that holds up just as well as the home made ones. I usually make mine with meringue powder. i have seen the mixes from wilton but have never tried them. Do they have one that is already mixed? Also, what brands do you guys recommend? I need them to decorate cookies. Thanks in advanced. 

I've had great results using premade RI mixes.  I've used CK, Wilton, and Baker's Kitchen.  I do sift the mix once or sometimes twice before adding the water because it makes it more homogeneous and breaks up any lumps.