Have not tried them, but some options are:
- GWAPower: a statistical power calculation software for genome-wide association studies with quantitative traits
- GWASpower/QT: a statistical power calculation software designed for genome wide association studies (GWAS) with quantitative traits in natural populations
- The GenABEL suite
Unsure on which platform the first two run (possible Windows only); GenABEL is popular with the R user community (cross-platform).
See also the CRAN task view for more R-based genetics packages.
We use Quanto for traits like triglyceride levels in blood and body mass index, assuming no family relationship (very important not to overlook!) and an additive model. We also use Quanto when considering gene-environment interactions in the power calculation.