Continuous Servo

What would the code look like to simply have a servo just continuously spin

You need a modified servo to spin continuously. There are instructions various places on the internet.
Here's one: Dios — Kronos Robotics
(note that there are two common types of "continuous rotation" modification for servos. In one, all the servo electronics are removed, turning the servo into a gear-motor that has to be controlled with a relatively high-power motor driver. The other (as in the link above) leaves the electronics intact so that the motor can be controlled by a logic signal, but removes mechanical feedback so that the electronics can no longer figure out what the motor position is, and just keeps trying to reach it.)

And here's a message about driving such a modified servo from an Arduino:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1251100597
(hmm. Haven't tried it was the newer servo library...)

I have it spinning
Here is my code but I would like it to go slower

#include <Servo.h>

Servo myservo;

void setup()
{
myservo.attach(9);
}

void loop()
{
myservo.write(1500);
}

Here is a test sketch you can use to check for the values to set the desired speed. Connect a pot to analog pin 1 (see: http://www.arduino.cc/en/Tutorial/AnalogInput) and note the values printed on the serial monitor as the speed changes. Writing this value to the servo will set that speed.

#include <Servo.h> 

// connect center pin of a pot to analog input 0
// connect outer pot pins to +5V and Gnd. 
// for more on how to wire, see: http://www.arduino.cc/en/Tutorial/AnalogInput
 
Servo myservo;  // create servo object to control a servo       
int sensorPin = 0;    // select the input pin for the potentiometer
int stopped = 90;     // tweak this to a value that results in no servo rotation 
int pos = stopped;    // variable to store the servo position 
int oldPos;           // used so that only new (changed) values are printed  
 
void setup() 
{ 
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object 
  Serial.begin(9600);
} 
  
void loop() 
{ 
 // read the value from the sensor:
  int sensorValue = analogRead(sensorPin);  
  pos = map(sensorValue, 0,1023, 0, 180);
  myservo.write(pos);  
  if(oldPos != pos) {
     Serial.println(pos); // only print when pos changes
     oldPos = pos;
  }
  delay(100);
}

note that the latest servo library will work in degrees or microseconds, this code uses degrees