Buy this pen. It's the Paper Mate InkJoy 300 retractable ballpoint pen. It has a medium point and it writes smoother than every single pen I have ever used. This is not a light endorsement! THIS IS THE BEST PEN YOU CAN BUY. And right now, you can buy a 24-pack for just $8.92. That comes out to about 37 cents per pen. That's 37 cents that won't eat at your heart when the ink runs out. Plus, it's retractable and that's just a good feature to have.
NOTE: This is not a paid post. I honestly really like this pen and wish most people would use it so they don't have to suffer through life using mediocre writing devices or worry about giving up their life savings for something that writes when you need it to.
NOTE2: This pen does not write well upside down. So if you're writing while upside down, well, don't. That's weird.