A relatively simple thing we did was replace the kitchen faucet. The kitchen was renovated fairly recently (within the last 10 years), so there is not a lot we were planning on doing with it. The old faucet was leaking from the handle a bit when turned on, and a bit ugly. It was also a bit short for the sink, making it hard to fill up pots etc sometimes.
Under the sink, the lines from the faucet were soldered to the supply lines, and only the cold side had a shut-off valve.
For the new faucet, I used flexible lines to make the connection and added new quarter-turn shut-off valves.
The faucet itself we got on sale at Canadian Tire, and it has the pull-out handle with the sprayer, and works quite well. This was a quick, relatively easy project and it made surprisingly big improvement to the overall look of the kitchen.