I recently met the creator of the iDo Wedding Planning Software at the Association of Bridal Consultants state meeting.  I can't even begin to describe how impressed I am with the software. 

The structure and work flow is meticulously thought-out and there are tons of time-saving features.  The guest list management and invitations features will save you enough time to make it worth the investment.  (It's only $30.)

All that said - the details are below.  Check it out and download a free trial.   

(My background is actually in web-based software sales, so I've been behind the scenes in software for years - this is good stuff!) 

~ Kerri Smith, NittanyWeddings.com  

iDo Wedding Couple Edition is wedding planning software designed to help save time and energy while planning a wedding. From compiling your guest list to mailing the last thank you note, your wedding will be a success. Brides and grooms across 55 countries have enjoyed using iDo to organize their wedding details.

You can visit the website and download the free 30-day trial.