I tried the 555-based step up circuit last night, just to see how I got on with it using the parts I had on-hand... it worked surprisingly well! For the 555 stage I used:
R1 & R2 = 100ohms
C = 0.22uF
And for everything else:
Diode = UF4007
MOSFET = 2SK2718 (pulled from an old dot matrix printer)
L = 470uH
Setting my bench supply to 7.2V I was getting well over 700V on the output with a current draw of around 100mA, and it charged a small bank of photoflash caps very quickly 
Think I might build a permanent version, it's got to be useful for something!