The historical goblins were actually pretty powerful faeries. D&D took it's idea from Tolkien, making goblins weak, but even in Middle Earth, goblins are very dangerous. Of course, compared to a 0-level human, goblins are pretty dangerous. Adventurers over level 3 pretty much laugh at them, though. That annoys me, a bit.
1. Goblins have faerie blood. They can all use minor magic. Maybe give them one level 1 spell, such as Dark. Or grant them limited invisibility once per round.
2. Have goblins get level 1 thief skills for free. I think this would work well, and make them nastier without going overboard.
3. Have them use poisons regularly, so that anyone struck by them will be making a Saving Throw.
4. Hobgoblins would be older, tougher goblins. Maybe give them up to 4 Hit Dice, with more Hit Dice meaning they are older and tougher. Any given group will likely have a hobgoblin in it. He would also have access to whatever special abilities normal goblins have.
5. Since goblins are fae, maybe they are neutral or even friendly with elves. This kind of leads to a Summer/Winter Court scenario, though. Evil elves might work with goblins, and they wouldn't automatically hate each other. And maybe some few goblins are actually good guys. Not sure I like that, but it's an idea.