Well, Pokemon that's both fast and defensive really isn't that great. A wall have no use of speed, and a sweeper should try to focus more on Atk than defense. Then there is the issue of what a good stat is and what is valued more, def or Spe. However, there are some that can be good defensive Pokemon and still maintain a decent speed and be competitively viable.
Gliscor is a prime example of a speedy tank, with decent HP and Spe and fantastic Def. Access to Poison Heal and a excellent defensive typing makes Gliscor a great option.
Dragonite may not seem like a very bulky Pokemon, but its wondrous Ability Multiscale allows it to survive almost any hit. It's access to a wide variety of coverage moves and power makes it more of a Attack based Pokemon, but its still no lightweight on the defensive front.
Miltank may not look like much, but used under the right circumstances it can be a excellent defensive Pokemon. Once again its Ability Thick Fat and reliable recovery is the main selling point, allowing it to take almost any Fire attack with ease.
Espeon might not like much, but its Speed and excellent support movepool allows it to work as a great supporter.
Venusaur might need sun support to gain any real speed with its Chlorophyll Ability, but once in the Sun it can be a true behemoth with good typing and good support movepool. And with the introduction of Mega Venusaur in XY, it can be even more dangerous tank.
I will add more momentarily.
