Best equivalent for IsInteger in SQL Server

What is the best way to determine whether or not a field's value is an integer in SQL Server (2000/2005/2008)?

IsNumeric returns true for a variety of formats that would not likely convert to an integer. Examples include '15,000' and '15.1'.

You can use a like statement but that only appears to work well for fields that have a pre-determined number of digits...

select * where zipcode like '[0-9][0-9][0-9][0-9][0-9]'

I could write a user defined function that attempts to convert a varchar parameter to an int within a try/catch block but I'm checking with the community to see if someone has come across any succient methods to achieve this goal - preferably one that can be used within the where clause of a SQL statement without creating other objects.

Late entry that handles negative

ISNUMERIC(zipcode + '.0e0') --integer
ISNUMERIC(zipcode + 'e0')  --decimal

For more see this

1 approach is

zipcode NOT LIKE '%[^0-9]%'

Double negatives, got to love 'em!