There is a great interactions checker at Drugs.com
http://www.drugs.com/drug_interactions.html
You just enter your medicine list, and click Check Interactions and all drug-drug and drug-food interactions come up, with an indiction of the severity of the interaction and how they should be managed.
The medicine list can also be saved - this is a great feature - so that you don't have to re-enter the meds everytime something changes.
I keep a list running for each of my parents and it works really well.
JJ