How can I make a toggle switch for two LEDs?
The 555 can either source or sink quite a considerable amount of current (like 200mA). Thus the transistor shown in the circuit isn't necessary (IMHO) for something like an LED. You can connect one LED from + to the output and another from output to GND. Like this:



Note - I've a feeling that the 555 doesn't have a high value that's equal to Vcc but slightly less than it. Which means that when LED2 is on, LED1 might be a little on too (anyone?)