Speck Candyshells.
They come in a bunch of colors, are easy to find in stores or on amazon, provide great protection, and take little away form the overall look and shape of the phone. The big thing is that they are generic enough to be able to be used in all environments (work or social) yet provide a distinct amount individuality becase of the colors.
While I persoanlly have a ton of cases and like some of the more "exotic" offerings like the aluminum cases mentioned above or even some of the other case companies that aren't mentioned, I found that most of those cases are situational. Not to mention that aluminum bumpers are disturbingly expensive for what you actually receive. They look great usually but the return on investment is merely visual.
In general the bumper style cases (this includes the aluminum bumpers too) don't provide enough protection overall while a case like the Otterbox Defender offers an overkill of protection. The Candyshell to me has been my go to case since late August and fits every situation I have come across. So much so that even though I own more cases than 90% of the posters (I have a huge Rubbermaid tote full of cases), I still use my original Black Candyshell I bought when I picked up my iPhone 4. True I have bought/received a couple other colors but my black one is still my favorite and most used. It is on my phone now actually albeit a little dinged up since it has been on phone through multiple vacations and work trips. Still fully functional.
Anyway, whatever you decide, good job for being a cool mom. 4 iPhones aren't cheap.
