ne555
the best thing I ever done was to get circuit simulator software which helps you experiment and modify existing circuits for free without having to buy parts untill you know you got a working schematic and all values then you just print out a partslist and go shopping.
A good one is “Circuit Shop” 2 by cherrywood systems another I used in college was “electronics workbench” you can find a trial version of both online though full versions of this kind of thing are between 100 and 500 US there eh-hum might be hacked versions lieing around on lime wire too if you L@@K for them…
I use the circuit shop then found an internal schematic of the 555 that I made a file for then when I want to experiment with a timer in a circuit I copy paste it in and connect up then hit the simulate button to see if it works and debug untill it does work…
Good luck!