There's only one notebook on the market today that has an eSATA port (a big 17-in Asus.) So, you will have to use a PCMCIA or PC Express eSATA adapter - and that itself becomes a choke point.
That not withstanding, the best one I have found is the NexStar eSATA case with your choice of drives in it.
Are sure sure you don't just mean a SATA notebook HDD, i.e., 2.5" (Internal)?