Here is the help for the function radians which I think will do what you want. i.e. cos(RADIANS(180)) will return (-1)

RADIANS
Converts degrees to radians.

Syntax
RADIANS(angle)
Angle   is an angle in degrees that you want to convert.

Example
RADIANS(270) equals 4.712389 (3p/2 radians)

BigH,
I don't know of a way to get Excel to operate in degrees, but I find it convenient to put the formula =PI()/180 in an unused cell which is physically quick and easy to designate, such as Q1, then =sin(30*PI()/180) can be input as =sin(30*q1) It isn't perfect, but it saves a lot of strokes.  Hope this is helpful.

I must admit, I felt the same way until I started concerning myself with arc lengths and other measurements that are computed using radians.

There really is no way to force degrees by default.

Use the RADIANS() and DEGREES() functions to convert between radians and degrees.
 
gearguru

To clarify...

Excel's default anglular measurement is radians. Whenever I set up a spreadsheet where I'm initially using degrees I start with a column of angles in degrees. The next step is to convert these to radians (e.g., +A1*pi()/180 goes in cell B1). From then on, any computations refer back to the table of converted angles, that, I might add, may be concealed so that it appears you're working in degrees.

In the cell B1 you can simply enter
=SIN(RADIANS(A1))
or whatewer calculations you need. There is no need for converting the angle and only then work with it. Unless you want to.
You can also hide the column with the angles converted to radians, if you want to go step - by step in your calculations. You can not avoid the radians in any programming language, try to live with it.
gearguru

In excel you can write functions just like you can write a macro.
I don't have excel on this computer, so I can't look up just what it looks like, but it would be something like this:

function dsin(angle as number);

x=sin(radians(angle);

return(x);

end;

Or something like that.
Look up the help in excel. It is fairly straight forward. You can put it in one of the global module things, so that it doesn't matter what spreadsheet you have open it always has that function available.
You can write functions called dsin, dcos, dtan or whatever. (make sure you don't use function names that are already used).

I have found writing your own functions to be very helpful.
When I was working in a geotech lab we had all our report sheets in excel using macros, but if you went in and changed a number you had to make sure the macro got run, or else all the results were wrong. Macros take a long time, so you couldn't just set cells to run it each time any cell in the spreadsheet ran.
I wrote some functions that calculated USCS classifications from gradations and found proctor maximums from a curve fit  and such things. They calculate just like normal excel formulas and are quick and calculate in the background if you are typing a mess of data (instead of waiting or losing typing inbetween cells as things calculate).

Writing functions is also useful for loops and complex equations where it is a pain to reference many cells over and over again.

If you want me to look up what the exact function would look like, let me know and I'll do it sometime when I'm at home (we have corel suite at work for some reason).