These might be possibilities.....
- http://www.meritline.com/iphone-3g-usb-cable-162---p-29059.aspx
- http://www.meritline.com/iphone-usb-cable-car-wall-charger---p-39053.aspx
Watch out for those meritline cables! I bought a couple back in April 2008, and while they do somewhat work for charging (although not with bumpers on an iPhone 4), they do not work for syncing with iTunes. The sync starts, but always fails early on with an unexpected disconnection. I've relegated those two cables to car charging duty, where they are partially successful--charging is intermittent, and I am distracted as the begin-charging chime sounds repeatedly, and the display lights up every time it starts or stops charging. The cables are just junk, and now that I've installed a bumper (making them completely useless), I think I'll just throw them out.
I've recently ordered some cables from monoprice, and while those also don't fit with bumpers installed, they appear to be fine cables, otherwise. They do allow a successful sync, for instance.
So, I'm curious to hear how those meritline cables that you ordered work for you. Has their quality improved in the past couple years?