Here's some specialties to give people an idea of what you should look for. A specialty can't be vague and all encompassing so here are two examples of fields you might want to have a foot in but are too vague to be specialties on their own.

Like if you wanted to specialize in-
[u][b]Medical Science[/b][/u]
you could go with
[hr]
1. Psychology
2. Neurology
3. Physician (You know about the human body in general, which bones are hurting etc but nothing specific)
4. Toxicology(Overlaps with “Poisoning” but you'll be less deadly and you'll more often have the antidote than the poison)

or if you wanted a specialty dealing with-
[u][b]Assassination[/b][/u]
you'd probably go with-
[hr]
1. Sniping
2. Martial Arts(Hand to Hand or Armed(specify weapon))
3. Stealth
4. Poisoning(Can overlay with toxicology)


Remember that just because you have [b]1[/b] specialty, that doesn't mean it's your only skill. In fact, you can use your [u]specialty[/u] to give more power to [u]other skills[/u]. Like Neptune's skill in [u]acrobatics[/u] is strengthened by his specialty, [u]Martial Arts[/u], because of the honed balance and agility Martial Arts gives you. 

This is why it's important to pick skills that compliment your specialty and vise versa.