I'm having difficulties choosing a portable hard drive with so many options available in the market these days. Should I stick to the branded pushbutton ones like Maxtor, Seagate, etc or one of those build-it-yourself ones? Are there any distinct advantage between the two? What special features/precautions should I be looking out for?

The first question you should ask is what do you want to use it for? Is this a backup device, is it going to sit there and store photos and other files, are you going to travel with it...

Basically, I'm hoping to travel with a portable external hard drive rather than a notebook. With it, not only will I have a backup of my data, I'll have softwares & windows environment familiar to me when I plug it into any computers available. BTW, can I download data from memory cards if I plug a card reader into the drive, assuming it's powered?

Unfortunately it doesn't quite work like that for all too many reasons.

For starters, this probably violates the license agreement from M$.

Many notebooks will not let you boot from a removable hard drive. Especially older ones.

When you install Windows the drivers that get loaded are based on the hardware in the computer you're installing it from. Assuming you could take that removable drive and plug it in to another computer and boot from it, you are going to have a lot of trouble because the computer you're booting on has different hardware than the one you installed it from. This can be true even if the brand and model are the same... often times components like motherboards and chipsets vary slightly and may require different drivers.

If you install software to it and move the drive to a different computer, that software is probably not going to work correctly because anything that's stored in the registry is on the computer you initially installed it from. I'm thinking that this would also violate the license agreement for most software.

If you plugin a memory card or a pen drive then you can certainly copy the data from the card to the removable drive.

Would you mind checking out the "Seagate FreeAgent Go" Would this product fulfill my requirements?

A real slick concept but you have to make sure that the software that you're going to run is on their list of supported software. If your software is on there then this looks like it should be pretty decent and some of the reviews I read were pretty favorable. To be honest though I was not impressed with their list of "approved" software. Creedo Software List

You can add Install Anything for $20 and that's supposed to allow you to "install anything" but I didn't see any reviews for it.
Argo software is another add on.

Keep in mind that it's the Creedo software that's providing this functionality and you can purchase that separately. Creedo will also work with a USB flash drive which makes it all the more portable. - Just don't lose the flash drive ;)

I'd recommend downloading a copy of Creedo Personal and see if it passes muster. If you do, let me know what you think of it.

Thanks for the useful comment. However, browsing at the list of ceedo program directory already turned me off. I checked out the Argo "add any programs" but like you commented, no reviews or consumers feedback... may not be what it hyped up to be...