Speedo - get an electric one - stick a magnet to the disk and the sensor on the fork and then you dont have to worry about speedo drives etc. Also, it can be configured to your wheel size so you can get fairly accurate reading.
Interestingly, in the UK, you are not legally required to have indicators on your motorcycle. However, once fitted it is a legal requirement that they work properly.
This is from eBay UK, but a search on eBay US will find similar
Digital Speedo
There are lots of different types, cheap to "how much!?"
Jeff