Yes, you still have to point your finger.
The spell Descriptive Text is separate from Somatic Components. Somatic components have a specific description and are part of casting the spell; the description of the spell is the result. In the case of fireball, it describes how you aim the spell; that does not make it part of the Components.
A spell’s components explain what you must do or possess to cast the spell...
A somatic component is a measured and precise movement of the hand. You must have at least one hand free to provide a somatic component.
A stilled fireball is castable without the Somatic components... but then follows the text of the spell. The "pea-sized bead" will be directed from your fingertip, wherever it might be pointed at the time.
It's worth mentioning that this is a completely reasonable thing for a GM to homerule the other way, so ask your individual GM if you think it would be more fun to allow mentally aiming the spell instead.
Furthermore, WotC even clarified in the Spell Compendium that "Grand gestures" indicated in spell descriptions are unnecessary for Stilled spells; there is a strong precedence for ruling in this direction.