For the internal HDD, go for the Samsung SpinPoint F3 1TB.

For external HDD 2.5", my current favourite is the WD Passport Essential SE (USB3) 1TB. Have 3 of those, so far so good. If you don't have a USB3 capable PC, then you can either still get this WD unit, so you can future-proof your investment (especially if you plan to upgrade your PC in the near future), or you can just get a USB2 external HDD (you can also buy the HDD yourself and put it into its own enclosure, which is my personal preference).

Usually I would go for a 2.5" HDD from one of the major manufacturers - WD, Seagate, Samsung, etc, I usually get the cheapest unless I hear something particularly good/bad about a particular model, and then get a cheap but decent enclosure to go with it. But since the USB3 drives are out, I've been buying the WD units. USB3 is so much faster.

Right now I am doing two simultaneous file copy actions:
1. RAID-5 internal HD array to USB3 Probox HD (WD Green) - averaging 46.3MB/s after 80GB out of 313GB transferred
2. USB3 WD Book Essential 3TB to USB3 WD Passport SE - averaging 26.2MB/s after 44GB out of 601GB transferred

Both the Probox and the Passport are connected on the same PCIe x1 USB3 card, while the Book Essential is directly connected on the motherboard's USB3 connector. Not sure if the PCIe x1 card is a bottleneck or not.