I missed this thread earlier, but maybe I should chime in now, because I have an iguana. This post will be about iguanas, so don't read further if you aren't interested... At the moment mine is about 3 feet long, and he is a free roamer (no cage, he can move around as he likes). He's very tame, a real sweetheart. He's never bitten anyone. There are some igs that do, but if you take the time to tame them when they're young, you can avoid being bitten. (And if you get bitten by a baby while you're taming it, it doesn't hurt at all.) I love my iguana. I can cuddle with him; he'll lay on my stomach and chest when i'm on my bed sometimes, and I'll pet him. He'll eat from my hand. Males can get very aggressive during their breeding season. Not all of them do. They'll have the first one around the age of 2, usually, which will be the easiest. They get a bit worse each time until the age of 5. That's usually the peak of aggressiveness in breeding season. Mine is 3 years old, and is not aggressive at all during breeding season, but he does show other signs of it...
But iguanas have a lot of needs. They're much harder to take care of than a corn snake. Besides the space issue, they need a hot area to bask in. This means you need a heat lamp. Another really important issue is UVB light. They can get UVB from direct sunlight (not through glass, which filters outhte UVB) or from a UVB lamp. Unless you live in a very warm area and can keep your ig outside all day, you need to buy a UVB light. They aren't expensive, and they look like fluorescent lights and fit in the same fixtures. But without the UVB, an ig can't absorb the calcium in the diet, and will get very sick eventually. Iguanas are vegetarians and need a varied diet including at least a few types of leafy greens like collards, dandelion greens, mustard greens, escarole, endive, etc... Plus other veggies like snow peas, green beans, carrot, squash, etc. They should have a few of the greens and a few different vegetables in each meal, every day. And when the ig is small, everything needs to be in tiny pieces. As it gets bigger, the food can be a bit larger. Iguanas don't chew their food, so it has to be in small enough pieces for them to digest easily when they swallow the piece whole.
Anyway, corn snakes are a whole lot easier, but both animals can be very rewarding as pets. Just make sure your dad does his research before he gets an iguana. There are already too many sick iguanas being given up because people didn't take the time to learn about them before they bought one.
Might I suggest a chemealian (sp). with all the rainbow colors...their magically delicious! 
