The tables below are extracted from from
http://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/RegExp

Specifying a template

The replacement string can include the following special replacement patterns:

Pattern Inserts
$$ Inserts a "$".
$& Inserts the matched substring.
$` Inserts the portion of the string that precedes the matched substring.
$' Inserts the portion of the string that follows the matched substring.
$n or $nn Where n or nn are decimal digits, inserts the nth parenthesized submatch string.

Special characters in regular expressions

Character Meaning
\

For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally.

For example, b matches the character 'b'. By placing a backslash in front of b, that is by using \b, the character becomes special to mean match a word boundary.

or

For characters that are usually treated specially, indicates that the next character is not special and should be interpreted literally.

For example, * is a special character that means 0 or more occurrences of the preceding character should be matched; for example, a* means match 0 or more "a"s. To match * literally, precede it with a backslash; for example, a\* matches 'a*'.

^

Matches beginning of input. If the multiline flag is set to true, also matches immediately after a line break character.

For example, ^A does not match the 'A' in "an A", but does match the first 'A' in "An A."

$

Matches end of input. If the multiline flag is set to true, also matches immediately before a line break character.

For example, t$ does not match the 't' in "eater", but does match it in "eat".

*

Matches the preceding item 0 or more times.

For example, bo* matches 'boooo' in "A ghost booooed" and 'b' in "A bird warbled", but nothing in "A goat grunted".

+

Matches the preceding item 1 or more times. Equivalent to {1,}.

For example, a+ matches the 'a' in "candy" and all the a's in "caaaaaaandy".

?

Matches the preceding item 0 or 1 time.

For example, e?le? matches the 'el' in "angel" and the 'le' in "angle."

If used immediately after any of the quantifiers *, +, ?, or {}, makes the quantifier non-greedy (matching the minimum number of times), as opposed to the default, which is greedy (matching the maximum number of times).

.

(The decimal point) matches any single character except the newline characters: \n \r \u2028 or \u2029. ([\s\S] can be used to match any character including newlines.)

For example, .n matches 'an' and 'on' in "nay, an apple is on the tree", but not 'nay'.

(x)

Matches x and remembers the match. These are called capturing parentheses.

For example, (foo) matches and remembers 'foo' in "foo bar." The matched substring can be recalled from the resulting array's elements [1], ..., [n] or from the predefined RegExp object's properties $1, ..., $9.

x|y

Matches either x or y.

For example, green|red matches 'green' in "green apple" and 'red' in "red apple."

{n}

Where n is a positive integer. Matches exactly n occurrences of the preceding item.

For example, a{2} doesn't match the 'a' in "candy," but it matches all of the a's in "caandy," and the first two a's in "caaandy."

{n,}

Where n is a positive integer. Matches at least n occurrences of the preceding item.

For example, a{2,} doesn't match the 'a' in "candy", but matches all of the a's in "caandy" and in "caaaaaaandy."

{n,m}

Where n and m are positive integers. Matches at least n and at most m occurrences of the preceding item.

For example, a{1,3} matches nothing in "cndy", the 'a' in "candy," the first two a's in "caandy," and the first three a's in "caaaaaaandy". Notice that when matching "caaaaaaandy", the match is "aaa", even though the original string had more a's in it.

[xyz]

A character set. Matches any one of the enclosed characters. You can specify a range of characters by using a hyphen.

For example, [abcd] is the same as [a-d]. They match the 'b' in "brisket" and the 'c' in "chop".

[^xyz]

A negated or complemented character set. That is, it matches anything that is not enclosed in the brackets. You can specify a range of characters by using a hyphen.

For example, [^abc] is the same as [^a-c]. They initially match 'r' in "brisket" and 'h' in "chop."

[\b]

Matches a backspace. (Not to be confused with \b.)

\b

Matches a word boundary, such as a space. (Not to be confused with [\b].)

For example, \bn\w matches the 'no' in "noonday"; \wy\b matches the 'ly' in "possibly yesterday."

\B

Matches a non-word boundary.

For example, \w\Bn matches 'on' in "noonday", and y\B\w matches 'ye' in "possibly yesterday."

\d

Matches a digit character in the basic Latin alphabet. Equivalent to [0-9].

For example, \d or [0-9] matches '2' in "B2 is the suite number."

\D

Matches any non-digit character in the basic Latin alphabet. Equivalent to [^0-9].

For example, \D or [^0-9] matches 'B' in "B2 is the suite number."

\n

Matches a linefeed.

\s

Matches a single white space character, including space, tab, form feed, line feed and other unicode spaces.

For example, \s\w* matches ' bar' in "foo bar."

\S

Matches a single character other than white space.

For example, \S\w* matches 'foo' in "foo bar."

\t

Matches a tab.

\w

Matches any alphanumeric character from the basic Latin alphabet, including the underscore. Equivalent to [A-Za-z0-9_].

For example, \w matches 'a' in "apple," '5' in "$5.28," and '3' in "3D."

\W

Matches any character that is not a word character from the basic Latin alphabet. Equivalent to [^A-Za-z0-9_].

For example, \W or [^A-Za-z0-9_] matches '%' in "50%."