[Issar]

As chipz says, Necro is a great starting point. Probably the least gear dependent class, followed by Mage. Necro has way more utility than a mage, who is pretty much a one trick pony. Enchanters are a great solo class, but they have a steeper learning curve. They are always welcome in groups as well.

If cloth casters are not your preference, Druids are another great choice. They have utility, solo really well and are not hugely gear dependent. At the highest levels, Shaman are the solo kings. However, they are a very gear dependent class.

If you're not a fan of clothies or priests, your options for effective solo are, Bards. Bards are great solo or in groups. They are not a gear dependent class in the least. They are categorized as a dps class, but it is universally known that their dps is pretty bad. They are the ultimate utility class that can dual wield and wear plate armor.

Other melee runner ups are ranger and shadowknights. Both are fairly gear dependent to effectively solo. Without significant gear neither class will level efficiently enough to compete with the above classes, but it can be done.