This is great, I only knew about Acolyte of the skin.
By my reading of the rules the following classes should also qualify
Dragon Devotee (only 2/5 casting, no caster level required, don't think any casting implemented in PRC)
Talon of Tiamat (no casting level required)
virtuoso (arcane caster level 1)
they all have no pre-req or "arcane caster level X" as requirement rather than "cast x levels arcane spells". All 3 have "+1 level of existing arcane spellcasting class". Talon of Tiamat would obviously be very flavorful for Dragonfire Adepts.
WARLOCKS AND PRESTIGE CLASSES
Warlocks benefi t in a specifi c way from prestige classes that
have “+1 level of existing arcane spellcasting class” or “+1
level of existing spellcasting class” as a level advancement
benefi t. A warlock taking levels in such a prestige class
does not gain any of his class abilities, but he does gain
an increased caster level when using his invocations and
increased damage with his eldritch blast. Levels of prestige
classes that provide +1 level of spellcasting effectively
stack with the warlock’s level to determine his eldritch blast
damage (treat his combined caster level as his warlock class
level when looking at Table 1–1: The Warlock to determine
eldritch blast damage) and his eldritch blast caster level (half
his total caster level from his warlock levels and his levels
in the prestige class that grant him an increased spellcasting
level). A warlock also gains new invocations known at
these prestige class levels as though he had gained a level
in the warlock class.
A warlock cannot qualify for prestige classes with
spellcasting level requirements, as he never actually learns
to cast spells. However, prestige classes with caster level
requirements, such as the acolyte of the skin, are well suited
to the warlock. A warlock’s caster level for his invocations
fulfi lls this requirement. See page 71 in Chapter 3 for more
details on caster level requirements, spellcasting level
requirements, and specifi c spell requirements for feats and
prestige classes.