Newegg.com - Computer Parts, PC Components, Laptop Computers, Digital Cameras and more!, whatever is cheap. WD is more expensive usually, but good. Maxtor makes good affordable drives. I currently have 2 Maxtor external drives. Look at the RPM speed, faster better! Also, buy what you need now, not what you need next year, because next year the price per GB will be cheaper than now. Some purchases you want to future proof, with drives, that should not be a consideration. Make sure you buy a drive that supports your computers interface, the laptop should have USB 2 ports, so stick with that, some drives use fire wire. Finally size of the casing matters if you plan on traveling with the drive, the WD book drives are great for that; nice and small and good against shock.
If you can wait for USB 3.0 standard to be established I would wait. You would get a transfer speed of 5 GB/second, which crush by 10X the best drives that are out there. Otherwise, any USB 2.0 based driver should work.
You might check places you wouldn't expect, like Target. A couple months ago I went in to pick up some shampoo and cat food, and walked past a Western Digital 1 TB external hard drive that was selling for around $60. I couldn't believe it but I snatched it up.
It may have been a mistake because I just checked their website and it is "out of stock." But WD is a good unit. They are selling for about $110 most places, but are being displaced by the 2TB units.
Since you will be constrained by the speed of the USB 2.0 port specs, either the 5400 rpm or 7200 rpm will completely saturate the bus. WD makes a nice little external drive called Passport that does not require an external power source, but they are expensive $/GB, but you don't have to carry around a power cable.
What make and model of laptop are you running to determine if you have an eSata port, which would be faster than a USB 2.0 drive?
I really don't mind having an external power source. My laptop is pretty much my main computer, I only have it because I was in seminary. So my external HD will be sitting in the same place at all times.