If you want to buy posters that are "custom" like from artist then I like the ones @Jobedu but if you want to make your own then you can go to @Doculand Center and have a design you want printed

Where can I customize glasses, shirts..etc?

Go to @Doculand Center they customize everything.

Where can I find cool calendars?

well personalizing your own calendar is pretty cool you should head over to @Doculand Center or @Custom Made Gift Shop to make your own

Where can I get a letter printed off from a usb?

@Doculand Center can take care of all your printing needs, including printing from a USB :)

Where can I find a place to make a personalized calendar?

You can make personalized calendars @Doculand Center or try @Custom Made Gift Shop :)

Where can I find the cheapest printing shop?

What do you want to priny. I dont know if its the cheepest but its good @Doculand Center .They r fast and professional!

Where can I print a company's name on pens?

@Doculand Center

Where can I customize my own t-shirt?

if you are drawing something or have a specific and artsy design try @Mlabbas. for something more simple, you can try @Doculand Center