How to check if column exists in SQL Server table

SQL Server 2005 onwards:

if exists(select * from sys.columns 
            where Name = N'columnName' and Object_ID = Object_ID(N'tableName'))
begin
    -- Column Exists
end

And an UPPER CASE version:

IF EXISTS(SELECT * FROM sys.columns 
        WHERE [name] = N'columnName' AND [object_id] = OBJECT_ID(N'tableName'))
BEGIN
    -- Column Exists
END