I was with rescuemycar.com for years at about £18 a year, had to call them out a few times and got a very good service!
Downsides are that you pay a £40 excess every time you call them out and they have a 16 year age limit.
For a younger car I wouldn't hesitate to sign up with them again.
Paying hundreds to the likes of AA or RAC for breakdown cover is ridiculous IMO and akin to staying with British Gas for your utilities and paying their rip off prices, just because it's British Gas!
I currently have an all singing all dancing any car/personal cover policy with Auto Aid which cost about £40-50, but I havn't had to call them out yet so I can't comment on their service.
Don't forget to check the comparison and cashback sites as there are often good deals to be had there.