You may all be aware of this company Swimshop but I got their catalogue today and it has a few neat training devices. The lap counter above and something called Timewindow which attaches to one "lens" of your goggles and allows you to view a digital counter which counts up to 20 minutes and is meant to be easy to star/stop. All for £31.50.
They sell loads of other training aids/swimwear etc and seem fairly priced. I got the catalogue as part of taking out membership for Swimfit so I'd assume they endorse Swimshop. They don't have a website but have an email address email@example.com or phone (01582) 562111 where you can probably request a catalogue.