Is there any good applications out there that can monitor my router(s) bandwidth usages? As alot of modern broadband packages are no longer unlimited and a tool that could monitor the bandwidth directly of routers would be brilliant.

Thanks for any advice in advance.

You network card should be able to tell you or the router will and can tell you how much has gone up or down. Better still there are some good ISP's around that often charge less and give more speed without user caps.

I was on zen for ages, I got 5 times the speed they offered with there limits for a few pounds less for unlimited. result!

Dont be scared to change your ISP

If you have a cheap $50 router, you can't really use it to analyze packets coming through... You will need to setup packed sniffer on your computer.
If you're using a cisco or linux box as a router, install something like RRD Tools, it would do exactly what you're looking for.

even cheap router will tell you the data sent and data recived.

Even if the firmware doesn't tell you on a cheap router, a lot of cheap routers can be flashed to run Linux.