I use <a href="http://www.fastspring.com/" rel="nofollow">http://www.fastspring.com/</a>. I too am UK based and this solution works nicely. They're US-based, but it means anyone with a credit card (US, UK or whatever) can pay for your software and FastSpring just wire the earnings to your UK account.<p>I find this to be a far better experience than PayPal, Google Checkout and some of the others. They have great support and a really nice, intuitive backend admin interface. I think their fee (which can be 5.9%+$0.95 or 8.9% flat) is well worth it.<p>It's certainly a good starting point, even if you then build a custom solution later.<p>Good luck with your venture.<p>EDIT: Spelling :P