What's good to cure rash from poison ivy and poison oak?

Poison Ivy. The best therapy is a prolonged dose of oral steroids, typically 10 or more days. Tapering steroid packs such as a 10 or 13 day "dexpak" is most effective. Shorter durations of steroids will often result in return of the rash.
Depends on severity. With less severe cases, like if it Just involves a spot on your hand, you can just use topical benadryl (diphenhydramine) cream or calamine lotion. For more involved cases prescribed topical steroids can be helpful. But as was mentioned previously for more severe cases oral steroids are often necessary.
Steroids. As dr. Vaughn said, steroids are the best. If you just have a few spots, then a cream will do the job. If it is widespread, steroid pills are absolutely the best way to go.