I have used Nutella chocolate spread - you can spread it on a vertical surface a bit off the ground so they have to reach for it a bit - it presents a better shot and they can't wander off with it - peanut butter is the same, other people swear by a tin of cheap cat food, just open the tin and leave it out and they'll go for it, still others suggest whizzing up cat food in a blender so again, there's no chunks for them to wander off with.
good luck, i do enjoy a bit of 'bait and wait' with rats - i do not like rats.
sminky