I came up with few ideas for 3 other classes that might be interesting:
1.Gunman-skill called "Double Trouble" wich allows to shoot double amount of bullets in the same period of time.To divide points(4 or 5) i see 2 options:
A) Skill lasts for about 20-30 seconds and each point increases bullet damage by 5% starting with 60% damage of normal attack (4 or 5 skill points total)
B)Damage is steady like 60-80% of normal attack and each point gives additional 5 second to it's lasting wich starts with about 15-20 sec.
In both cases it should cost about 30MP
2. Wizard-skill called "Immortality" which for a certain time makes him resistant to any attack(if in some point PVP will be added then this should not be possible there). About points-each one increase period time by 5 seconds starting with 15-4 points total. Totall cost should be at least 50MP since its powerful skill.
3.Archer-skill called "Fire Starter" which allows him to shoot arrows covered with fire that cause more damage with each skill point used on it starting with 70% and growing by 5% each-4-5 total. Mp should be about 40. Note:if fire bow(s) are about to show up in game at some point then you could change its colour to green or something like that.