There is a page with information about the current limits of Arduino pins. There's also a question on the Electrical Engineering SE site that addresses the current limits of the board overall.
From the accepted answer on that question:
The 5V output pin is good for ~400 mA on USB, ~900 mA when using an external power adapter
So that's more than the 100 mA you mentioned in your question. (But go read the whole answer; there's more good info there.)
The easiest way to split the power is to use a separate, regulated power supply.
Except for simple tests (e.g., a single small unloaded servo), I use the digital i/o pins only for very low current signals: buttons, status LEDs, sensors, serial communication, etc.
For example, to control an IR LED that can handle up to 50 mA, I'll supply power to the LED from the Arduino board's Vcc pin and control it with a transistor attached to a digital output pin. Drawing 50 mA from the board's supply is well under the limit, and the digital output pin draws practically nothing.
For more than one servo, I use a peripheral PWM controller that takes power separately. That peripheral is powered by a separate 5V 2A power adapter, which supplies the current to actually turn the motors. I send commands to the controller using I2C from the Arduino, which is running from its own power supply.