The folks at iSlayer have just released a new menu bar, similar to their brilliant iStat Pro widget for Mac OS X.
Their new product allows you to customise a menu bar to show statistics about your system including hard drive usage, CPU and memory utilisation, temperature, fan speeds and network usage.

Initially the CPU option shows every core as a separate box in the menu bar, but this can be compacted down to just one box. Useful if you have eight cores such as my Mac Pro. There’s quite a few different ways to show the data that the software collects and I’ve managed to get it reasonably compact.I
I’m going to trial it out for a while and see if I get used to it. I like my menu bar to be clean and tidy and I’m still weighing up whether this makes it look messy or not.