autoNumeric is a jQuery plugin that automatically formats currency and numbers as you type on form inputs. It supports most International numeric formats and currency signs including those used in Europe, North and South America, Asia and India (lakhs).
jQuery Price Format is a plugin to format input text fields as prices. For example, if you type 123456, the plugin updates it to US$ 1,234.56. It is costumizable, so you can use other prefixes and separators (for example, use it to get R$ 1.234,55).