Hi Steve, I have used a 720 nm IR filter with some success. In full sunlight this requires exposures in the 3-4 second range. This filter still let's some near IR colours through and you have to do the channel swapping in post. There is an example picture in my gallery of the results. I have also tried a 850nm IR filter which blocks more of the red spectrum but exposures using this filter were into the 2 minute range, but this was on a cloudy day. Still waiting for a sunny day to try it properly but it is constant rain and flooding in Cornwall at the moment. Hope this info helps.
I just bought cheap filters off EBay, not knowing what to expect. But the results we good. For the sake of 7-10 GBP per filter it gives okay results at a cheap price. Good to give it a go and if IR is something you enjoy then you could then invest in better filters or get a second hand cheaper body and have it converted into IR.