Hey there Hortman. Joel's got the right idea for species, but if you want something really bombproof, a hybrid is usually a little more vigorous than your average purebred species. Thus, hybrids of the species mentioned above are especially durable. N. x ventrata, a hybrid of alata and ventricosa, is a particularly ubiquitous plant. Very easy to obtain and raise, with attractive, sizable red pitchers. I believe that petflytrap.com here sells them, as well as some other good starter species. You can also look to
Barry Rice's CP FAQ for a list of recommended vendors, most of whom carry Neps. There's also a good primer on Neps in the 'FAQ Library' on Barry's site. Two other good Nep-culture resources are
Nepenthes Around the House and
Nepenthes for Everyone.
When choosing your plant, keep in mind that Nepenthes have different requirements depending on their natural range. They're generally partitioned into two groups, the lowlanders and the highlanders, based on the elevation that they're commonly found at. Lowlanders like it brighter and require fairly constant temperatures and humidity throughout the day and night to succeed. Highlanders tolerate less light and enjoy a temperature drop and humidity spike at night, making them preferable for most beginners (unless you live in a climate akin to those of lowland Neps.) Unless you want to buy a terrarium setup, I think you'll find highlanders much more rewarding. Some plants are occasionally referred to as a third group, the intermediates, and these can often succeed in both highland and lowland conditions.
Don't be intimidated! Neps are too much fun to miss out on. There are some difficult species out there, but if you do a little reading before you buy, you'll be able to select an easy one. The fact that you're even asking attests to your competence.
Even if you treat Neps horribly, many will endure. They might not produce pitchers or grow very fast in poor conditions, but if you even vaugely follow the instructions out there, your plant should stay alive.
Good luck, and have fun!
~Joe