The above examples are very simple, and there is a good chance you might have more complicated analyses requiring a sample size calculation. More advanced analyses might include:

• Analysis of variance (ANOVA)
• Analysis of covariance (ANCOVA)
• Many types of regression analysis
• Repeated measure designs
• Clustered designs

A very good and comparatively powerful sample size program is called GPower. It can be downloaded free of charge from here:

http://www.gpower.hhu.de/en.html

GPower can undertake sample size calculations for most of the above situations, and primarily uses effect sizes. It comes with an extensive help manual.

However, unless you are very familiar with the different type of effect sizes (and they can be complicated), it would be better to make some time with one of the biostatisticians.