Here is a flyback driver I designed. I wanted something powerful and very reliable (I hate replacing MOSFETs) and this is what I came up with. It's very straightforward. Basically we use a 555 timer as an oscillator to generate a square wave between 10-100khz. This square wave is amplified by the TC4422 gate driver chip (I used the TO-220-5 version). This then drives a gate drive transformer of a 1:2:2 ratio (that's 10 primary turns and 20x2 secondary turns) for a + and - 12V square wave on the gates of each of the power MOSFETs (IRFP260). Each power MOSFET sees the full supply voltage of 35VDC or so. If more power is desired you can short out Q5 which is just a simple variable voltage regulator. If even greater powers are desired you may use a higher current rated transformer for the power supply, or go for more voltage (150VDC is the max input to the half-bridge). Keep in mind the maximum ratings for the 2n3055 (about 60V and 2-3A maximum). So if a larger power supply is used, you can no longer use the variable regulator. The half-bridge is good to at least 450W with a larger power supply (I've tested mine at 90V at 5A). This is a very flexible driver and I use it for various applications, but it's sole function is to drive flyback transformers.
Construction (pictures are slightly out of date)