Some thoughts:
WF FvS would be my favorite.
- Both self and group healing, should you decide to group.
- Solid melee damage. Sure, not top tier, but solid.
- Some damage spells, primarily Blade Barrier.
- Insta-Kill spells.
- All the self buffing you could want.
- Great Damage reduction.
- Does not require great gear to be a good soloer.
- and most importantly: WINGS!
The WF Wiz, or Wiz/Rog also is great. Rog gives the options of traps and the Insightful Reflexes feat is great for cranking up your evasion save without needing to have a dex score. I also love my WF Sorc, but sorc doesnt have any synergy with rogue stats, so I wouldn't consider that splash.
Light Monks are great melee soloers, but are a bit gear dependent if you want to hold your own.
There are some fun pally and ranger builds out there who focus a bit on their healing spells to give them excellent self healing and survivability. Maximize spell and some healing gear can go a long way here.
Bards can be excellent soloers, particularly a solid warchanter which gives better melee dps than spellsinger or virtuoso, though the spellsinger gets a huge mana pool.