Suzuki got this segment started in 1999 with the SV650. The SV became a huge hit. For a number of years Suzuki offered the naked GS500 and Bandit 600, but those bikes were more of a traditional design. The SV combined the charisma of a 90 degree V-twin with an affordable price. Suzuki initially offered the SV in two flavors a completely naked model, and the SV650S which offers a half fairing, and more sporting seating position. Today the SV650S is a fully faired motorcycle. For 2008 Suzuki introduced another 650cc V-twin to there line up; the Gladius.
Honda had it's own 650cc V-twin; the Hawk GT. Debuting in 1988 the Hawk was ahead of it's time and never really caught on in the states. Ten years later, in Europe, Honda introduced the Hornet 600. The Hornet wasn't available in North America (as the Honda 599) until 2004. However the 599 didn't catch on as much as Honda hoped it would, and was dropped from the US line up in 2006.
In 2004 Yamaha released their FZ6, a smaller variation of their successful FZ1. The bike is sold in the US with a half fairing similar to the Suzuki SV650S. Elsewhere in the world the FZ6 is available as a "full" naked bike. The FZ6 has become one of the more popular bikes in this segment.
Kawasaki jumped in to the mid-sized game in 2006 with the ER-6. The ER was first introduced with a fairing in the United States, later the naked version sold in Europe became available, known as the ER-6n. Prior to the ER-6 Kawasaki offered the ZR750 in the United States, and in Europe today they offer a downsized version of the Z1000, known as the Z750.
Ducati has had a mid-size bike since the introduction of the first Monster; the M600. The Monster went on to become one Ducati's most successful products of all time, and the smallest Monster was one of the best selling models. Over the years the baby Monster grew from 600 to 620, to 695, and finally with the next generation Monster the 696.
Triumph also had a a "mini-me" version of their bigger hooligan bike. Shortly after Triumph entered the 600cc supersport category the entered the mid-sized hooligan bike market with a naked version. The Speed Four attempted to offer the thrills of the Speed Triple with a smaller four cylinder power plant. In 2008 Triumph revisited this formula using the fresh triple from the 675 sport bike creating a nice little package called the Street Triple.
Finally there's the South Korean upstart Hyosung. Hyosung has been trying to break into the US market with their 650R and S models. Esentially a copy of Suzuki's 650 V-twin design, the Hyosung tries to offer the performance of their Japanese rivals for less money.