The following chart was designed for the vaguely Christian cleric of typical pseudo-medieval games. You'll probably need to revise this chart heavily if you've got a lot of weird gods in your campaign.
Random Cleric Advancement
Start with a normal undead-turning, no-spell-at-first-level cleric. Advance hit points, to-hits, saves, and turn undead normally. For each new spell slot you would normally gain, roll on the following chart instead.
01-05 You gain +1 to hit instead.
06-15 You gain +1 on all saves instead.
16-62 You gain a spell slot as normal.
63-65 Your ability to Turn Undead increases by one level.
66-68 You gain the ability to convert one memorized spell per day into healing of d6 per spell level. If you roll this at 2nd level you can heal d6 as a daily power.
69-70 You start to hear voices. Once per session you can ask them a question. The DM will roll a secret reaction roll check for you. The truthfulness of the answer will depend on the roll. Reroll if you get this result a second time.
71-72 You start to see visions. Once per session you can use clairvoyance, as per the 3rd level MU spell. If you roll this a second time, you may opt to use wizard eye (MU 4) instead, on a case-by-case basis. Reroll if you get this result a third time.
73-74 You are really getting into the smiting end of this business. Any time you roll maximum damage with a melee weapon, your opponent must save vs. paralyzation or be stunned for d3 rounds. Reroll if you get this result again.
75-77 You can turn something besides undead once per day. Roll on the chart below:
- Demons, devils, etc.
- Elementals of all sorts.
- Constructs and robots.
- Stupid mash-up monsters like owlbears and dracolisks
- Elves and fairies
- Anything cthulhoid and tentacley
Your DM will have to decide the equivalency on their turn charts, based roughly on hit dice. If you get this result again, roll on the above chart again. If you get an already-obtained result, your ability to turn that kind of monster goes up to 3x per day. Reroll anything that is already 3x per day.
78-79 Fanatical Followers: Any henchmen or hirelings you obtain who do not already have a strongly documented faith gain +2 morale from your contagious religious fervor. Reroll if you get this result again.
80-81 Create Holy Water: So long as you can cover the cost of 1gp each for the vials, you begin every new adventure with d6 holy waters. Reroll if you get this result again.
82-84 Declare a Crusade: Pick a single species of monster or other type of foe that really cheeses you off. All your party members are +1 to hit and damage against these creatures so long as you are standing with them. This works up to and including massive army scales. You do not get the bonus. If you get this again you must declare a new crusade against someone else. The old bonus no longer applies.
85-86 Last Rites: If you spend 1 turn and sprinkle holy water on a corpse, it cannot return as undead (excepting the occasional revenant). This has no effect on corpses that are already undead. Reroll if you get this result again.
87 Power Marriage: You can declare any two sentient beings to be united in holy wedlock, and they will totally go for it, as if they had been in love the whole time. You can do this exactly once. Reroll if you get this result again and haven't already used it.
88-89 Pilgrimage: The thing you seek, the MacGuffin or whatever, is located in the tomb of a saint nor more than 4 play sessions away. You must have a fair shot at it--like any other treasure, but there's no guarantee you will get it. If you don't get it by the fourth session you can keep trying or let it go and roll again on this table. However if you choose to roll again and then you do get the thing somehow anyway, you lose whatever gimmick you rolled. The DM must think up some clever reason why.
90-91 Some servants of the Lord have strange gifts. Roll on the magic-user spell table equivalent to the highest level spell you can cast. Add that spell to your own spell list. If you don’t have any spells yet (e.g. you’re rolling for second level), gain a random 1st level MU spell as a daily power.
92 Future Saint: The site of your death becomes holy. No undead may enter there and any of your faith who rests here regain spells in half the usual time. Oddly, this still applies if you are resurrected or raised (don't tell the pilgrims). Reroll if you get this result again.
93-94 You gain a spell slot as usual AND a bonus slot of the level below it. If you were rolling for a first level slot, you gain two first level slots.
98 Word of your holiness has spread. When travelling through the countryside, peasants will be happy to feed and shelter you and your friends in exchange for your divine presence. They will also hide you from Johnny Law. The jaded inhabitants of the city require a favorable reaction roll for you to pull this off. Reroll if you get this result again.99-100 When you are really in the soup you can call on an angel of the Lord (or whatever) to help you. Throw two six siders. Those are the levels of the wandering monster charts the DM should roll dice on. The DM should combine the two monsters in as horrific a creation as possible (contact with the divine is often terrifying). Additionally, the creature can fly 180’, is immune to non-magical attacks, and has one special power of the DM’s choosing. It probably glows, too. It will perform one service on your behalf, subject to DM interpretation, or join in a single combat. If you are not in dire straits when you call on it, it will arrive in its vengeful form: roll a third monster to combine with it and now it wants to smite the shit out of you. You can call on the angel but once. Reroll if you get this result again and have not summoned the angel. (I.e. you can't bank more than one angelic bail-out.)