hi Peter,
Sorry, i didn't explain about the procedure that i followed.
I use the 5V reference voltage provided on the UNO board as the energy source for all the sensors.Yes, i use a bread board to make the connections.I use jumper wires to make those connections(they are only few cms in length).I also ran a small program to check the voltage that i was getting from the 5V pin, and it was 5.0V. I connected a wire from 5V pin to the bread board.I then made parallel connections to three analog pins from the bread board and found out all the three pins read 5.0V .
But then, I noticed a strange thing. when I removed the 5V connection, those pins started to give out random voltages ranging between 1.5V to 2.0V(seems mysterious).
Later, I connected those sensors and ran the program.It was then that i encountered the problem. Temperature sensor was acting weird. Just to check, without removing any hardware connections, I ran a program to sense temp alone. It gave a constant output at 24.90 C. i ran the previous program again and there was the same problem with the temp sensor. the temperature varied drastically. Sometimes it would shoot upto 41 C n sometimes come down to 19 C.
I ran another program just know what was going on.I found that when i run humidity and temperature sensor together there was no problem. humidity sensor was connected to digital pin and LM35 to the analog pin. but when soil moisture sensor and LM35 were run together there was the problem with LM35( both were connected to analog pins A1 and A5). I hope u got a clear picture of what is going on.
I tried your code to get the raw values from the temp sensor.this time i got consistent output :)!!. But the value that i got was pretty high.(temperature is around 25 C in my city).
rawADC:649, temparature:316.89soil moisture:1023.00.
humidity:43.00%
temp:24.00
rawADC:650, temparature:317.38soil moisture:1023.00.
humidity:42.00%
temp:24.00
rawADC:650, temparature:317.38soil moisture:1023.00.
humidity:42.00%
temp:24.00
rawADC:648, temparature:316.41soil moisture:1023.00.
humidity:42.00%
temp:24.00
rawADC:649, temparature:316.89soil moisture:1023.00.
humidity:42.00%
here's the code once again
#include "DHT.h"
#define DHTPIN 2
#define DHTTYPE DHT11
DHT dht(DHTPIN, DHTTYPE);
void setup()
{
Serial.begin(9600);
dht.begin();
Serial.println("Weather Sensor");
}
/*void temparature()
{
float temp=analogRead(5);
temp=temp*5*100/1024;
Serial.print("temparature:");
Serial.print(temp);
Serial.println("^C");
delay(2000);
}*/
void temparature()
{
int rawADC = analogRead(5);
Serial.print("rawADC:");
Serial.print(rawADC);
float temp = (float) rawADC * 5.0 * 100.0 / 1024.0;
Serial.print(", temparature:");
Serial.print(temp);
// Serial.println("^C");
delay(2000);
}
void moisture()
{
float moist=analogRead(1);
Serial.print("soil moisture:");
Serial.print(moist);
Serial.println(".");
delay(2000);
}
void humidity()
{
float humid=dht.readHumidity();
float t=dht.readTemperature();
Serial.print("humidity:");
Serial.print(humid);
Serial.println("%");
Serial.print("temp:");
Serial.println(t);
delay(5000);
}
void loop()
{
temparature();
moisture();
humidity();
}
I hope i was clear in explaining the problem. 
Thanks.