Was talking to Mark before, and told him about HPI checks being forced down in the price, even HPI themselves are now offering them at £19.99 instead of the £39.99 they used to charge, so Mark said I should make a post on the forums as it may come in helpful for people when buying cars.
All these companies are legit, and have plus and minus points to their service, but all in all, they are using the same database as the standard HPI check service:
The original service, the most comprehensive, they wont check imports, but they do more checks then most competitors and also offer indemnity insurance. £19.99 Per CheckRAC Car Data Check
A cheap service offered by the very respected RAC, but not very comprehensive to say the least... Covers the basics and includes indemnity insurance, but other then that, its not really worth it except for price. £5.00 Per Check MyCarCheck.com
The lowest priced provider of vehicle checking services, and probably the best all rounder. For the price, it is certainly the leader, and it offers most things a proper HPI check covers. It does not offer indemnity insurance, but does as a bonus cover imports. £3.95 Per Check
The key to it all is, if you are buying a car worth a considerable amount, go the full hog and get an HPI check if you are on the brink of paying for it. This then covers you and gives you best piece of mind. Remember, when buying from a garage, they should really do a check before selling it on, but may not do as its not a law. So remember to ask the specific questions, has it had an HPI check, is it clear of all elements of the check, ask what elements their checks include etc... If they havent done one, ask them to.
The RAC check has only one good thing, the indemnity insurance, but doesnt cover as many aspects as the cheaper check by MyCarCheck.com.
Overall, MyCarCheck is the best imho, as this can mean anyone can get an HPI check for any car, affordably, and is also forcing the likes of HPI to reduce their pricing. Get a check done by these guys, but use your nod, if the car is of a considerable value, consider a full HPI check on top of this before you hand the cash over, just for peace of mind more then anything.