Ok, I admit the question was a bit ambiguous. For me, all answers posted so far have some validity.
Chihiro rightly points out limitations of using 15 significant figures as the result displayed is larger than the max value which needs 17 figures to enter as in the link of vletm. I think you can use this formula to get the same result entered in A1, say:
=2^1023*(2-2^-52)
Special double values like infinity and nan could be argued to be larger, eg:
=INF()>A1
=ISNUMBER(INF())
both return TRUE but then such values do not have a finite value, similar to cardinal / ordinal distinction in maths.
Using an addin (xNumbers perhaps?) as per GraH Guido 's suggestion you might be able to use:
=REPT(9,32767)
Or an even larger number using a text floating point representation which would be much larger than those above.
The point of questions like this is really just to raise an interesting and lively discussion as well as hopefully learn something new!