This is the best one I have come across. I haven't joined, but I have seen a page once in a while and it's pretty complete. I did just try to join and we'll see if they ask for money. LOL!
naturaldatabase.therapeuticresearch.comI just came across this one:
/www.standardprocess.com This one has surprised me with as many herbs as are covered:
reference.medscape.com/drug-interactioncheckerwww.anniesremedy.com Most just list a few herbs at a time, so I usually search for drug interactions with that specific herb to cut down the amount of time wasted looking at all the other sites that say they have herb-drug interactions.
Hopefully others will have some good links!