Hey I've decided on a solenoid for my project, it's DC 24V 0.8A. I know from the tutorial I'll need a transistor, diode and resistor. What are the proper ones for this solenoid? Amazon links would be super so I can get it all at once 
Thanx in advance
Too many to list. I would get a to220 transistor rated 5amp or so. at 0.8amp, you are pushing the envelope of the avr's current capabilities. I would put a 110ohm resistor on the gate or go with a mosfet.
A 1n400x diode would be more than sufficient.
thanx dhenry. I'm afraid you only managed to confuse me tho lol. I've been searching around but I dont enough about it to select the right one.
Can someone please post a link to ones that I can purchase?
The 'Motors, Mechanics and Power' section of the forum would be the ideal place to ask this question and you are likely to get better help there.
The transistors listed in the tutorial (TIP121 or TIP102) would be suitable for that solenoid. A more modern solution would be to use a mosfet instead - lots to choose from, for example STP40NF10L.
Darlington would work
you only managed to confuse me tho
something at which dhenry excels.
High current super-beta switching transistors like the STX724 might do - min gain 80 at 1A, feed it 30mA or so to saturate so base
resistor of 150 ohms. However there isn't much overhead in the voltage rating.
The even better (but more expensive) ZTX851 will only need 15mA of base drive and saturate to about 0.05V.
Darlington will be cheaper (but larger and run much hotter)