For a more direct reply in the spirit of the question - d20Modern has a whole range of special weaknesses for supernatural creatures, and you could find some useful ones amongst them
From the SRD
Creature Weaknesses
Although a creature’s type and species determine many of its traits and abilities, GMs are encouraged to alter a creature’s physiology, behavior, abilities, tactics, and defenses when it serves the story or to confound players who think they know everything about their opponents.
The rules provided allow GMs to build custom monsters and ascribe special qualities to them. When designing a creature, the GM should also think of ways the creature can be defeated. From the heroes’ point of view, a creature’s weaknesses are more important than its abilities. Assigning weaknesses to creatures gives under-powered or poorly equipped heroes a fighting chance.
Table: Sources of Weakness lists many sources to which a creature may be vulnerable. A source can be a specific object, location, substance, sound, sensation, or activity. How the creature interacts with a source of weakness is left up to the GM, although most sources must be in close proximity to the creature (if not touching the creature) to affect it. GMs may roll randomly on the table, choose a source that suits the creature, or devise their own.
Source Effects
After determining a creature’s source of weakness, the GM needs to decide how the creature reacts when confronted by the source. Pick an effect that seems appropriate for the creature and the source.
A creature gets either a Fortitude or Will saving throw to overcome or resist the source of weakness; the DC of the save varies depending on the source’s strength:
Strength of Source Save DC
Easily resistible 10
Moderate 15
Strong 20
Overpowering 25
Creatures usually react to a source of weakness in one of six ways:
Addiction: The creature is compelled to ingest, imbibe, or inhale the source. The source must be within 5 feet of the creature to affect it. On a successful Will save, the creature negates the compulsion. On a failed save, the creature spends a full-round action indulging its addiction, then may resume normal actions while suffering one or more of the following effects (GM’s choice):
• Creature takes a –2 penalty to Dexterity and Wisdom.
• Creature takes a –2 penalty on attack rolls and skill checks.
• Creature loses 10% of its current hit points.
• Blindness: The creature has a 50% miss chance in combat, loses any Dexterity bonus to Defense, moves at half speed, takes a –4 penalty on Strength and Dexterity-based skills, and cannot make Spot checks. Foes gain a +2 bonus on attack rolls to hit the creature.
• Deafness: The creature takes a –4 penalty to initiative checks and has a 20% chance of spell failure when casting spells with verbal components. The creature cannot make Listen checks.
• Creature loses one of its extraordinary, supernatural, or spell-like special qualities.
Each effect lasts 1d4 hours. Even creatures immune to mind-affecting effects are susceptible to a source-induced addiction.
Attraction: The creature is compelled to move as fast as it can toward the source. On a successful Will save, the creature resists the compulsion. On a failed save, the creature moves toward the source at its maximum speed, taking the safest and most direct route. Once it reaches the source, the compelled creature seeks to possess it. If the source isn’t something the creature can easily possess, it gets a new save every round to break the compulsion.
Even creatures immune to mind-affecting effects are susceptible to a source-induced attraction.
Aversion: The creature finds the source repellant. On a failed save, the creature cannot approach or remain within 1d4 x10 feet of it. In the case of traveling sounds, the creature moves away from the source as fast as it can, stopping only when it can no longer hear it. On a successful Will save, the creature overcomes its aversion and may approach the source freely.
A repelled creature that cannot move the requisite distance from the source suffers one or more of the following effects (GM’s choice):
• Creature takes a –2 morale penalty to Strength and Dexterity.
• Creature takes a –2 morale penalty on attack rolls, damage rolls, and skill checks.
• Creature takes a –2 penalty to Defense.
• Blindness: See Addiction, above.
• Deafness: See Addiction, above.
• Creature loses one of its extraordinary, supernatural or spell-like special qualities.
Each effect lasts until the creature leaves the affected area and for 1d4 rounds afterward. Even creatures immune to mind-affecting effects are susceptible to a source-induced aversion.
Fascination: The creature finds the source fascinating and ceases all attacks and movement upon seeing, hearing, smelling, or otherwise perceiving it. On a successful Will save, the creature negates the fascination and can act normally. On a failed Will save, the creature can take no actions, and foes gain a +2 bonus on attack rolls against the creature. Any time the creature is attacked or takes damage, it gets a new save to negate the fascination. Otherwise, the fascination lasts as long as the creature can see, hear, smell, or otherwise perceive the source.
Even creatures immune to mind-affecting effects are susceptible to a source-induced fascination.
Fear: The creature is frightened by the source. If it fails its Will save, the creature flees from the source as fast as it can. If unable to flee, the creature takes a –2 morale penalty on attack rolls, weapon damage rolls, and saving throws. On a successful save, the creature overcomes the fear and can approach the source or otherwise act without penalty.
Even creatures immune to mind-affecting effects are susceptible to a source-induced fear.
Harm: Contact with the source or proximity to the source harms the creature in some fashion. On a successful Fortitude save, the creature negates the effect or, in the case of instant death or disintegration, takes damage instead. GMs may choose one of the following effects or invent their own:
• Blindness and deafness: See Addiction, above. The blindness and deafness last 1d4 hours.
• Creature loses all of its supernatural and spell-like special qualities.
• Creature is turned to stone instantly.
• Creature loses 50% of its current hit points.
• Creature drops dead. On a successful save, the creature takes 3d6+15 points of damage instead.
• Creature is disintegrated. On a successful save, the creature takes 5d6 points of damage instead.
Even creatures immune to effects that require Fortitude saves are susceptible to source-induced harm.
Table: Sources of Weakness
d% Source
01 Alcohol or moonshine
02 Amber
03 Animated cartoons
04 Archways
05–06 Bells or chimes
07 Books written by William Blake
08 Bunnies
09–10 Cancerous organs
11 Carbonated soft drinks
12–13 Cats
14 Chrome
15–16 Classical music
17 Clocks
18 Clowns
19 Cocaine
20–21 Country music
22–23 Crosses or crucifixes
24 Crows
25 Dogs
26 Elvis Presley memorabilia
27 Fast cars
28 Fast foods
29–30 Fluorescent lights
31 Games of chance
32 Gold or iron pyrite (fool’s gold)
33 Grave dirt
34–35 Heavy metal music
36–37 Holy symbols
38–39 Holy water
40 Hospitals
41 Ice cream
42 Insecticide (DDT)
43 Jack o’-lanterns
44 Keys
45–46 Laughter of children
47 Laundry detergent
48 Lavender
49 Lilac-scented candles
50 Mathematical equations
51 Morphine
52–53 Nerve gas
54 Nitrous oxide (laughing gas)
55 Novocaine
56–57 Number “8”
58 Pearls
59 Penicillin
60 Photo flashes
61–62 Plastic or vinyl
63–64 Played violin or electric guitar
65 Playgrounds
66–67 Plutonium
68 Poppies
69 Pulsing strobe lights
70–71 Radiation
72 Radio waves
73 Rubber
74 Running water
75–76 Silver
77 Sodium benzoate (food preservative)
78–79 Sodium chloride (salt)
80–81 Specific phrase or word
82 Specific song
83 Spoken Latin
84 Stuffed animals
85 Sumerian or Egyptian hieroglyphs
86–87 Sunlight
88–89 The Bible
90 Tinfoil
91–92 Toxic waste
93–94 Triangles
95 Television infomercials
96 Television static
97–98 White rice
99–100 X-rays