Thanks for the replies. Most of my books are very small and this is not normally an issue but i recently purchased the Mother Earth News Archive (1970-2012) in mobi format and some of the years are over 50MB as one file. Sounds like USB or the content server may be my best bet for now. Alternatively, as one poster alluded to, you can copy the mobi file to the My Kindle Content folder under My Documents to add to the Kindle. The link for doing this is here
http://www.howtogeek.com/howto/13169/
For some reason, it doesn't appear that Kindle for PC will let you just drag and drop the mobi file directly to the program. Thanks again for the suggestions.