I personally imagine that litecoin will be the next big cryptocurrency, atleast for GPU miners. As the ASICs ship out the difficulty will soar and miners using GPUs will move on, likely to the next biggest cryptocurrency, being litecoin. Although, people with FPGAs will be unable to mine litecoin due to the fact that it uses scrypt and as a result it is likely that, if they wish to continue mining, they will move their miners onto one of the other SHA-256 based cryptocurrencies, such as PPCoin and Terracoin.