I too use NavBox Pro, but for most other flight planning I just use the NATS and MetOffice GA sites. There are a ton of iPhone / iPad apps that can help you. Whatever you use, always put lines on maps, and use it to make sure anything computer generated is sensible either vertically or laterally.
If you feel drawn to using a whizz-wheel to do time / distance and basic flight planning calculations, then I would recommend replacing it with a ASA CX-2 electronic computer. Its so much easier and accurate than those old whizz-wheels. I got mine about 6 years ago and I am sure it was about £100 at the time. TransAir currently have them for £64.95, which I think is very good value.