With DDO there are literary unlimited possibilities when it comes to class, race, feats, skills and builds. It all comes down to preferences and playstyle in the end. But if you are looking for a strong solo / leveling class build for DDO, here are some suggestions:
Warforged Wizard / Sorcerer ( Optionally multiclassed with 1 or 2 Rogue levels)
Going either Wizard or Sorcerer with a Warforged will give you very high survivability mixed with very high DPS. A very good combination for leveling. With the Repair line of spells you can even heal yourself as a Warforged, and when you get the Wall of Fire spell at level 7wiz / 8 sorc you will be a killing machine, quite literary.
Key Strengths:
- Repair (Heals)
- High Dps
- High Survivability
- 1 or 2 levels in rogue will give you the option to wield more weapons and a wider variety of skills that can help you while soloing (Open locks, disarm traps etc)
A good example of this build can be found here : http://forums.ddo.com/showthread.php?t=218205
Favored Soul (Warforged works best)
Favored Souls are able to solo most things in the game. They have great heals making them very good at surviving, along with some very nice damage spells like Blade Barrier
Key Strengths:
- Good Healing
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Damage Spells (Blade Barrier)
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Instant Kill Spells
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Good Buffs
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Damage reduction
A good example of this build can be found here : http://forums.ddo.com/showthread.php?t=268346
Paladin (Dwarf or Human)
This is one of the easier choices if you want to solo / level up fast. Paladins have very high survivability and decent DPS.
Key Strengths:
- Immune to Fear and Disease
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Good Heals
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High Survivability
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Easy to play
A good example of this build can be found here : http://forums.ddo.com/showthread.php?t=327669