Electoral Calculus (Not a tactical voting site, but gives you more insight into your constituency, which can help you be sure the two above are giving the best advice.)
If you’re really not happy with the party the tactical voting sites recommend for your constituency, Compass are also offering the Win As One vote swapping tool, where you can be paired up with someone who also can’t vote the way they would like to. By swapping votes, both people can do what they have to for a tactical victory while still having their first choice counted.
It is definitely worth checking all three of these to make sure your tactical vote is used in the best way possible:
GetVoting.org
StopTheTories.vote
Electoral Calculus (Not a tactical voting site, but gives you more insight into your constituency, which can help you be sure the two above are giving the best advice.)
If you’re really not happy with the party the tactical voting sites recommend for your constituency, Compass are also offering the Win As One vote swapping tool, where you can be paired up with someone who also can’t vote the way they would like to. By swapping votes, both people can do what they have to for a tactical victory while still having their first choice counted.