There are many romanization schemes for Cantonese. One of the most difficult things for learners is to handle the multiple systems. Unfortunately there has been no well-established standard like Hanyu Pinyin. Here's a brief listing of common schemes:
Yale: Used by many textbooks for second language learners of Cantonese. It is easily recognized by the use of a silent "h" to represent syllables that have tones in the low register and the use of tone diacritics similar to Hanyu Pinyin. This website uses a version that was modified by Matthews and Yip (1994).
Sidney Lau: Another method based on the Yale system that has been used in textbooks but not as popular as Yale.
Jyutping: Promoted by the Linguistic Society of Hong Kong to be the standard romanization scheme, and used predominantly in the linguistics literature. One of the pluses of this scheme is that it only uses the letters of the English alphabet and numbers. Thus, it is easy to type. But few non-linguists have adopted this system and it has some characteristics which makes it unintuitive to English speakers because of the difference between Cantonese and English.
IPA: Also known as the International Phonetic Alphabet. This is a romanization system used by linguists and is designed to transcribe any language in the world. Because it is a standard system, it can be useful to compare other romanization schemes to. However, it does not make the ideal system for learners because it often requires memorizing more symbols than needed.
Hong Kong Government: Not suitable for foreign language training because there is no one to one mapping of sounds and symbols, although this is affected by the perception of Cantonese phonemes by English speakers. Nevertheless, this is the romanization you will see on street signs and place names in Hong Kong.