Another vote for Ride With GPS - for road riding at least. I use it quite a lot to navigate a route I haven't ridden before.
If you follow the instructions and export as a TCX file you will get turn 'prompts'. Although as noted above you only get an audible warning when you are at the turn (unless you pay). The way around this is you get an extra screen which lists all the turns and the distance from the next turn. Keep an eye on that and you'll know when you are getting close.
The other thing to be aware of is you don't get the turn prompts unless you plot the route on the website. If you upload a GPX or whatever you don't get the 'turns' listed. Something to do with plotting the route on Google map and the API goes away and gets the prompts.
Another tip when plotting a route is click just before / after a turn to make the route go through the turn, rather than clicking on the turn / junction. This guarantees the turn is prompted.
Bear in mind it's only as good as the map data, occasionally you won't get prompted to turn, or prompted to turn when on a straight section of road! The Garmin does however loudly complain when you go off course!