If the spreadsheet values are in latitude and longitude units, then you have to plot them in a 'geographic' coordinate space (which is measured in latitude and longitude).
To do it interactivly, create a new data frame in geographic coordinates (and wgs84) and run Create Feature Class-> From XY Table in that frame.
Save the output feature class and define its coordinate system appropriately (as GCS_WGS_1984). You can do that by exporting it from your GCS_WGS_1984 data frame, using the data frame coordinate system, or through the Properties menu when you right click the new FC in ArcCatalog (or by using the Toolbox Tool).