If you want to purchase a new consumer or prosumer-grade drive, here are some points to keep in mind:
1. Make sure the drive has at least a 3-year warranty.
2. Browse hard drive reviews and product recommendations, including those from magazine publishers. If you're in the market for a low cost drive while getting the most storage capacity for your dollar, buy a drive that's been on the market for a few months.
3. Check with small local PC shops & colleagues, and online ratings to find out which drives and/or manufacturers should be avoided. Verify the manufacturer and/or reseller has a good reputation and established procedures for returning broken or defective drives.
4. Calculate the cost per gigabyte of the drive by dividing the total price(including any applicable taxes or shipping surcharges) by the drive's capacity in gigabytes. I'll use the 250GB drive I purchased as an example:
250GB 7200 RPM 8MB Cache IDE Ultra ATA133 Hard Drive 74.99
shipping & handling + 5.64
=$0.32 per gigabyte
Compare the price per GB(in this case 32 cents) to other drives with similar features(SATA or PATA, noise levels, RPM, areal density). Take into account the aforementioned points and make your purchase.
Internal or External?
If you need an external storage device, then go buy an internal hard drive and put it inside an external enclosure. Works well for hard drives and DVD/CD Burners...