I highly recommend you to visit **[Pathguide][1]** to get a sense of how vast is the catalog of Pathway Databases. Looking into the category **[Pathway Diagrams][2]** or in **Transcription Factors / Gene Regulatory Networks** should help in your task.

I would start by looking at these DataBases:

- GeneMania
- BioCarta
- WikiPathways
- Reactome

If you are working with a species other than human, perhaps you'll find a more suitable database in PathGuide.

Good luck!

PS: Sorry New user limitations impede me to post more than two links :/
  [1]: http://pathguide.org/
  [2]: http://pathguide.org/#4