When shopping for the right rug, if you're not a designer, figuring out where to start can be a little daunting. Only recently have major home brands started offering carpets, and there is such a wide variety and historical richness in styles, that it's hard to know which one works for you.  Here are some great jump-off points:

If there was a goddess of textiles, she'd be Madeline Weinrib. I go to her first for carpets, pillows, and fabric. If she doesn't have exactly what I'm looking for, I leave her site having some good ideas for where I want to go. Always an inspiration, and usually a complete drool-fest. I hope you love as much as I do!

Every striped dhurrie you can imagine is available at Dash & Albert. A quick word about wool vs. cotton - wool anywhere you're having a party and cotton anywhere you're hanging out barefoot is generally my rule of thumb. Cotton doesn't hold up as well, but is naturally a little softer and very cozy feeling.  Wool holds up well over time, is easier to clean, and is heavy enough, that it wont need to be relaid every time a pair of heels walking back and forth on it for a night.

ABC Carpet & Home. This is where designers start when they want every selection on the face of the earth available - at good quality. This is from their new Cobble Hill Sisal collection. These people seriously know a lot about rugs.
 
A word on some of the different carpet styles here:
DHURRIE
I'm a sucker for a great dhurrie - they're the flatweave summery ones that you love at your beach cottage or thrown on top of a wood floor to soften things up. I put them in my kids room, my living room, and running down the hallways.
PILE
These carpets are on a backing, so they can be made in any shape and style your heart desires. Essentially the fabric is hooked through the backing, then cut so that the freyed ends are the soft pieces of fabric you walk on. These are great if you need a custom shape, or a complex design. They are especially cushy, but sometimes fall a little flat for me (just being honest) - I do however have an oriental style in my bedroom!
SISAL
These are made of courser natural threads like Jute or, of course, Sisal. They are a little rough underfoot, but the texture more delightful than anything unappealing. They can be a larger style weave because the material is so resilient, or relatively small weave.
Always be sure to check that your rug is responsibly produced. Because of the detailed nature of the weaving, be especially careful to avoid child labor when shopping for your next carpet. There is no umbrella governing body, so just ask or contact Good Weave if you're more comfortable getting professional advice!