Some of the best deals to be had are from the online parcels brokers - yesterday I received a 25kg, two box consignment from the other side of the country. I booked and paid for the delivery.
It came on TNT, booked through interparcel.com - cost was change out of £16 for a 24 hr service. Booked direct with TNT it would have cost £55, and with ParcelFarce, £50.
Another good online co. is parcel2go.com - £6.90 is their typical small parcel charge for a 24 hr service.