Typically it is more inexpensive (and more cost effective to maintain) to assemble an external drive oneself with the use of an external enclosure and a desktop sized drive.
Desktop hard drives are easily found for approximately $0.50 to $0.70 per GB, at least in the US (apologies for not being more global). IEEE1394a enclosures are fairly inexpensive (under $40, again in USD), and provide 400Mbits/s throughput - more than ample for most tasks, even running applications. There are only a handful of chipsets available, the most popular being the Oxford 911. If one follows this route, make certain the enclosure employs the newer version of the Oxford 911 chipset, which supports the ATA6 standard, ATA133 compatability, and 48-bit LBA addressing allowing for drives larger than 137GB (currently tested up to 300GBs or higher).
If speed is of absolute importance, one might consider IEEE1394b (also known as Firewire800), which provides 800Mbits/s of transfer; however, the enclosures are more costly, and would require an IEEE1394b PCMCIA card to provide Firewire800 connectivity.
One note regarding LaCie branded drives : LaCie makes use of proprietary adapters (with a power brick) to power their devices. Most of the "better" enclosures utilize a standard power supply cable, and are easily replaced, if necessary.