Today I spent some time trying various Excel formulae and have I consolidated the list that I consider useful for general purpose. I hope this can be useful to others as well.
AND - Logical AND Operator
AVERAGE - Averages the number in a range
AVERAGEIF - Average based on some condition
AVERAGEIFS - Average based on multiple conditions
CONCATENATE - Joins strings
COUNTA - Count number of cells that are not empty
COUNTBLANK - Count blank cells
COUNT - Counts the number of cells that contain numbers
COUNTIF - Count based on a certain condition
COUNTIFS - Count based on multiple conditions
DATE - Returns date
DELTA - To check if the two values are equal
EXACT - To check if two strings are equal
FALSE - Returns logical value 'False'
HYPERLINK - Creates a link
IF - Checks a condition
IFERROR - Returns a particular values if there is some error
INT - Rounds a number to the nearest integer
ISBLANK - Checks if the reference is blank
LARGE - Returns the K-th largest value
MAX - Returns the largest number from a Range
MIN - Returns the minimum value from a range
MONTH - Returns the month
N - Converts a non-number value to number
NOT - Logical NOT
NOW - Returns the current date and time
OR - Logical OR
PERCENTILE - Returns K-th percentile
PERMUT - Returns the number of permutation
POWER - Returns the value of a number raised to a power
PRODUCT - Multiplies numbers
QUOTIENT - Returns the integer portion of a division
RAND - Returns a random number
RANK - Returns rank of a number in a range
REPLACE - Replaces a part of string
ROUND - Rounds a number to a given number of digits
ROW - Returns the row number of a reference
ROWS - Returns the number of rows of an array reference
SIGN - Returns the sign of a number
SMALL - Returns k-th small value of a range
SQRT - Returns the square root
SUM - Adds numbers
SUM - Conditional sum
SUMIFS - Sum based on multiple conditions
TEXT - Converts a value to text
TIME - Returns time for the given values
TODAY - Returns current date
TRIM - Removes spaces from start and back of a string
TRUE - Returns logical true
TRUNC - Removes decimal points from a number
TYPE - Returns the type of a value
UPPER - Converts a string to upper case
VALUE - Converts a text string that represents a number to number
VLOOKUP - Looks for a value in the left most column and then returns
corresponding value from other column
WEEKDAY - Returns weekday