The Jensen VX6020 will go to 32GB, not sure if the front input is what you are looking for. It has a front SDHC slot so I just put everything on a 32GB SD card. Sweet!
I had a Kenwood Excelon with a rear USB but I can't recommend it, went Tango Uniform and Kenwood needed it back to fix it so now I have the Jensen. I ran an iPod on that, glad to be rid of it (iPod). (Well glad to be rid of the Kenwood too. The UI was bizarre).
its best to just do sd cards, i have a usb reader on the usb dongle using sd card 16gb and another sd card inserted in the head unit for another 16gb and i have multiple 16gb sd cards to change out
16gb memory sticks are like 10$. I like using smaller memory sticks because head units tend to read the small ones faster and I can keep 4 or 5 sorted by category.