It's tricky, there is a heavily enforced permit system in the residential streets around the stadium. If you want to park as near to the ground as possible then you can try your luck on Longford road for a pub or profiteering local retailer.
If you spend over 25 pounds at the retail park next to the Ricoh and then display the receipt on your windscreen you'll be ok. Otherwise try street parking around 'Jubilee Crescent,' the centre of Radford, and just outside of the permit area and take a taxi up towards the Ricoh. From there it'll be at most about 3 quid.
For taxis, central taxis on 02476 666666 is pretty much the best on offer.