My cable lock is jammed. The key fits in but won't turn. What can I do? My bike is locked up outside on the street so I guess the first thing would be to put a second lock on it in case the first randomly comes unlocked.
This depends on where you are to some extent.
I would start by asking either the local police or council and if they're not interested a locksmith. Going with someone official makes the job look a lot less sketchy.
Might be worth while having the receipt or some photos of you and the bike handy incase you're challenged.
That said, most cable locks are pretty worthless and if you're not worried about getting stopped, some quality cable cutters or small bolt cutters would do the trick.
And, yours isn't, but for combination locks, you can usually decode them by pulling on the lock body and turning the barrels gently until you feel a click.