I've done a few searches on Google and tried a few examples but have had no luck. I'm limited to formulas and arrays as my settings at work don't allow Macros. If a Macro is the only way to this I can probably get that changed.

I have multiple sheets with URLs in Column A, for example:

Sheet1
google.com
yahoo.com
facebook.com

sheet2
google.com
myspace.com

sheet3
yahoo.com
msn.com

I'd like to take all the data and merge it into 1 column on a summary tab. I'll be adding to the other sheets in the future and there is good reason they are separate lists. So I'd like sheet4 to have:

google.com
yahoo.com
facebook.com
myspace.com
msn.com

It grabs all the URLs and removes duplicates. Is there an easy way to achieve this?