This schematic shows several ATtiny85 minimal circuit configurations. The ATtiny85 is shown using its internal 8 MHz RC oscillator, which divided by 8 gives a 1 MHz system clock, and with an external crystal and ADC buffer. The ATtiny85 has 8kB flash, 512 bytes of SRAM, and 512 bytes of EEPROM.
Here you can find the current ATtiny85 datasheet
The internal oscillator has a base accuracy of +/-10%, which is great for most applications, but if you are doing any critical timing, a crystal can get the accuracy to +/- 0.001%. Hooking a crystal to an ATtiny85 will use two of the four total ADC inputs. The reset line takes another, leaving no lines to select an SPI device. This circuit takes advantage of the programmer's assertion of reset to disable the SPI EEPROM during programming, and enable it when the programmer lets reset go. Of course this only works with a single SPI device, but sometimes one is all you need.