Best place for exchanges w/o receipt?

[BearAddict]

I just received a Blu-ray player as an early Christmas present and have some unopened DVD's that I purchased recently that I would like to return for the Blu-ray version. The problem is that I no longer have the receipts. Where have you had the best luck returning items w/o a receipt for either a comparable one or for store credit?

We received Planet Earth last year from my uncle but it was the Blu-ray version. We had a nightmare trying to enchange it for the DVD version w/o a receipt at places like Target. We even told them we would eat the difference since the Blu-ray version was more expensive but they said they couldn't do it.