First Date of next quarter

You can use the =Date(year, month, day) formula.  The day and the year are both fairly easy, the trick is getting the month right.  I've got two solutions. 

Nested if statement:

There are 4 quarters in a year, so you'd need at least 3 'if' statements.  It would look something like this (where A1 is the date your referencing)

=Date(year(A1), if(month(A1)<4, 4, if(month(A1)< 7, 7, if(month(A1)<10, 10, 1))), 1)

To translate:

It won't change the year.  As for the month, if your original date is Jan-Mar, then it will set the month to April.  Otherwise if your original date is Apr-Jun, then it will set the month to July.  Otherwise if your original date is Jul-Sep, then it will set the month to October.  Otherwise it will set it to January.  The day will always be set to 1.

Nested if statements are messy, and it's very easy to lose track of all the brackets.  However you should just be able to copy/paste that formula into your sheet, and just update the cell references.

The second solution is using a vlookup.  It looks nicer, but requires you to use another sheet.  Would look something like this

=Date(year(A1), vlookup(A1, table_array, 2, false), 1)

Where the table_array is on another sheet and is just a list of the months (1 - 12) with the corresponding 'quarterly months' in the second column.

Hope that answers your query.

EDIT: I realised I didn't handle the year correctly.  If the month is Oct-Dec we will be moving into the new year so will want the year to increase by 1.  The revised formula is:

=Date(if(month(A1)>=10, year(A1)+1, year(A1)), if(month(A1)<4, 4, if(month(A1)< 7, 7, if(month(A1)<10, 10, 1))), 1)