We’ve been playing with both Dropbox and SkyDrive ( the larger GB paid versions ) and have had good luck with both so far - at your size/scale, they might work well. We’ve adjusted our perception to think of those as servers sitting in the corner instead of who-knows-where.
Dropbox obviously has a jump on SkyDrive but since we’re slowly switching to Win 8 I thought it pertinent to keep it in the running. Common access, organizing folders and sharing are all easy and straightforward so far.