First some basics - There is a difference between a face mask and a respirator. The best analogy I can come up with is the difference between a window and a screen. A face mask is like a screen, it keeps out the big stuff. A respirator is like a window, it will keep out most stuff but not everything... which brings us to the N95 designation. 'N95' simply means that the mask keep out 95% of test particles - it's the best you can expect really unless you move up to something military grade and then you're looking at spending big bucks, and sticking out like a sore thumb.
Which protection is best for your preps? As is generally the case, this is a matter of opinion... and everyone has one. My thinking is this - Ideally, I'd love to have 100 N95 respirators on hand per person but they run about $1 apiece and right now they're hard to find due to the H1N1 virus. 5 per person would be a nice, attainable, affordable goal. If you just can't get your hands on them, or can't afford them, then face masks are an affordable alternative and better than nothing.
In the case of H1N1 - according to the CDC site - face masks/respirators are not necessary in most cases. As they have repeated many times - regular, proper hand washing will do more to protect you than a mask.
Here are a couple of links to the CDC and FDA which will help you make an informed decision about your options.
- http://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/n95list1.html - this link has a list of NIOSH approved N95 masks. Most of the ones on Ebay seem to be approved including (but by no means limited to) 3M, Kimberly Clark (aka "KC") and SAS brands. The list also includes direct links to the manufacturers (where available) and PDF downloads of "Donning Procedures" (i.e. "how the heck do I put this thing on?")