Small characters face a number of disadvantages. They can't use two-handed weapons, and have to use two hands to wield a versatile weapon ^DDI.

Further disadvantages include:

• The inability to Grab Large creatures (medium creatures can).
• The inability to Bull-Rush Large Creatures (medium creatures can).
• A shortened vertical reach when jumping (one-third of the creature's height is added to athletics checks; the smaller the creature, the shorter the reach).
• Very limited options for 'Change Self' type rituals and powers, as they specify the new form must be your size category.

Are there any benefits to make up for this?

I am looking for benefits specifically supported by the rules, rather than anything that relies upon the DM being amenable to particular interpretations. Joe's answers are useful for the latter purpose, but were not what I was looking for clarification on.