Extra Ruger factory mags for the LC9 are relatively inexpensive and readily available; cost is around $25.I'm really torn between the Ruger LC9s and the new S&W M&P 9 Shield:
http://www.smith-wesson.com/webapp/wcs/stores/servlet/Product4_750001_750051_831056_-1_780153_757781_757781_ProductDisplayErrorView_Y
I must admit the two magazines included with the Shield is weighing heavily in it's favor.
It would be nice if Ruger would put a LC9s model with three mags in the line-up like they have done with the SR22:
http://www.ruger.com/products/sr22PistolDE/specSheets/3611.html
The Shield 9mm is another top choice in my book. It's handling characteristics with the 8 rd mag are better than with the short 7 rounder. The availability of extra 8 rd mags is spotty to scarce with a good price for them being around $30.
IMO you can't go wrong with either a LC9 or a Shield.