Best - send them off to be professionally scanned.
Most cost effective - flatbed scanner with a proper film scanning hood.
To be honest, it depends very much on the end use of the digital image. If it's just for posting on the internet, a relatively cheap scanner will do the job fine. If you're after big (A4 or bigger) prints, you'll probably want to spend a bit more and get something better - possibly a dedicated film scanner. It won't be a quick job though.