I have a series of values and I need to test if the returns are > 0. The t-test assumes normality, so I was wondering if there are other alternatives. Note that the standard suggested sample size is >30, what if you have less than that? What other statistical procedures can one apply to determine significance in small sample sizes which can ether be parametric or non-parametric.
First, there is no lower limit to sample size for the t-test; in fact, it's mostly used when N < 30. When N > 30 the t-distribution looks just like the Normal.
Second, if, by "series of values" you mean a time series, then the t-test is not appropriate – you need some method that accounts for the dependence of the data.