1. Wait until the iPad is actually released here, and Apple finally add the apps to the UK store.
2. On iTunes, sign out of your account and change to the US store. Then register a new account with the US store, using a US address and US credit card.
3. Same as option 2 but without required a credit card linked to a US address. Go on eBay, buy US gift cards, use these cards to sign up for a new account on the US store. You still need to use a US address, but won't need the credit card.