Here is my ultimate holder setup.
Get a hybrid case around $5-$10
Get an Arkon Mobile Clamp
Get a Camera mount.
that is the setup I use for my S2 (I will get picture tomorrow)
Here is a case for your S3 $7 shipped
I won't use any other case if I can help it. I have "tested" this case and it really works. Was taking pictures of a wasp nest in my gas tank cap cover. normally bee's ignore you as long as you don't frak with them. NOT THE CASE for wasps. at about 12 inches 5 or 6 of the 11 wasps broke off as a little squadron to investigate and teach me the error of my ways.
when I felt the wind from their winds I whipped my arm away and away went the phone 15 feet through the air into the street. Not a scratch. LOVE these cases (and they look good too)
For the mount. THIS is expensive but I have found nothing else I will trust short of building it myself.
arkon has this http://www.arkon.com/accessories/sma...era-stand.html
its about $25 shipped IIRC yeah its expensive but its NICE. stock it won't fit the S2/S3 in that hybrid case. look on the back at the spring REMOVE the spring. it will now open further. get one of those fabric elastic scrunchie band things for your hair. use that around the outside to compress the clip (I will take pictures tomorrow) EXTREMELY secure. I don't care how you ride it aint moving.
the one flaw is the ball joint losses tightness (a pity considering the price they command for it) I just slap a bit of electrical tape before popping it on.
and lastly is the mount. ditch the tripod (you could tape it to the handle bars like I did till my proper mount comes in)
you can get these around $4 a pop (I did not look deep I got 2 for $6)
Or something nicer
for just a couple dollars more (it splits in 2 so you can mount either a flash light or split off the extra and its a camera mount)
I have 2 of the plastic ones coming in the mail and one of the blue aluminum ones I scored for $9
that is how I would suggest mounting your S3 that IS how I am mounting my S2