This review is not directly relevant to using RNAi for screens, of course. But Fig. 4 is a nice summary of tools for disrupting miRNAs. And I like to try to keep up with aspects of RNA biology, as understanding RNA biology is interlinked with exploiting it as a research tool.
Garzon et al. (2010) Targeting microRNAs in cancer: rationale, strategies and challenges. Nature Reviews Drug Discovery 9: 775-789. Available FREE.