As Frank points out....what do you mean by large? I will assume you mean a snake that gets up to or exceeds 10 feet.
Obviously the big pythons (retics and burms) get large. I can't say they are a snake I would recommend to anyone as they really get TOO large.
Yellow Anacondas stay a reasonable size, but are not very personable on average.
Some of the Boa constrictor morphs get large (Suriname and Guyana boas, for example) and are usually docile.
Several larger Australasian pythons get in this range. Amethystine Pythons (and related species) get long, but are fairly slender. They aren't the best natured snakes, however.
Olive Pythons are big neat snakes that are apparently more docile.
Some of the carpet pythons exceed 10 feet, although many of the most common morphs (i.e. jungles) are smaller.
A large blood python is generally under 7 feet long but it is a HUGE snake compared to the other pythons. They are a neat snake if you want a large snake but don't want to have to house a 15 foot animal. All the bulk without the length!
Just a few ideas to consider. BTW - have you considered to cost of feeding/housing a large constrictor?
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Chris Harrison
San Antonio, TX