Classification of Active Galaxies I've read that there are 4 distinct although related forms of AGs : Seyferts, Quasars, Radio and Blazars. Are there any other forms possible? Also do these forms ever intermix to give something new?
Yes of course, there are other forms apart from the four stated above. Basically you have just two kinds: 


the radio-quiet, and
the radio-loud.


But then again, there are two Seyferts


Seyfert I, and
Seyfert II


Apart from Quasar, Blazar and Radio galaxy, we also have presently,


BL Lac (Named after its prototype BL Lacarte (original member of Blazar type)), and
OVV (Optically Variable Violent Quasar or OVV Quasar; subtype of Blazar)


Best source to begin with is wikipedia.org of course.