Chinese words with non-Chinese letters / characters?
There are lots of them, here's what I can recall:

T恤衫，T-shirt

X光片，X ray image

卡拉OK，karaoke

K线图，Candlestick chart

A型血，Blood Type A

P图(v.)，Photoshop an image

维生素C，Vitamin C

O型腿，Blount's diseas

TCP协议，Transmission Control Protocol

RSS源，RSS feed

UI设计，User Interface design

All of the words are widely used, most of them combine the English letter and Chinese so the word is easier to understand. Basically everyone knows the 26 English letters, so only the words are translated to keep things simple.