BaconReader for iOS offers a unique Explore feature that lets you search for new subreddits by subject. This can be very handy if you don't know exactly what you are looking for.
Tap the bacon icon in the upper left hand corner of the screen and select the Explore item. You'll see a list of various subjects/interests. Select one to see associated suggested or popular subreddits about that subject.
Find a subreddit you want to subscribe to? Tap the "i" button to the right of the subreddit name and tap "Subscribe."