23 and me
Last month, I spat in a tube, which was then shipped to California.
There are various services out there which will aim to find your long-lost relatives and tell you a bit about your health, but 23andme appears to be the biggest, so I gave it a go.
I wasn't impressed when their app told me that it "wasn't available in my region", but falling back to the website to register my kit worked. It took the best part of a month for results to come through.
The ancestry stuff is straightforward. This being the biggest such service, it would be surprising if it didn't find some distant relatives of mine - I got a wide range of likely third and fourth cousins scattered across the world. At some point I might transcribe my family tree into it sufficiently to see if we can confirm the connection. Nobody closer was unearthed, though (perhaps that's a good thing!)
And the health side of things? They're at pains to point out that nothing they provide is medical advice, and the site very sensibly insists on walking you through a mini tutorial on how to understand the results before revealing some of the more serious medical indicators. The thing I most enjoyed (reminiscent of GCSE biology) was the long list of recessive traits/diseases, i.e. things which you can carry and pass on to your children if your partner is also a carrier. In my case it turned out that I have none of the ones tested for, which is potentially quite reassuring.
It does cost a few quid, but you can halve the price if you don't go for the health stuff and just stick to ancestry.