It depends on if you want transient expression or long-term. Previously we have used both retroviral (for long-term) and Calcium Phosphate transfection (for short-term) with allot of success. If we knew specifically what you are trying to do (i.e. duration of gene-expression, just tagging cells or expressing a protein) we may be able to help better.

I often use liposome.

Cationic liposome-based vehicles should be quite helpful

I know that electroporation works well, but be careful about the work interest, if you are working on gene expression for instance, electroporation could modify it.