Cool! I'm no expert, but optics, aerospace, and defense mainly that I'm aware of. Airbus has a huge wing manufacturing plant in Broughton which I'm sure helps anchor the industry, they have massive tie-ins with the local universities through apprenticeships. Prototype mirror segments for the E-ELT project are also being built here[1] (last I checked; there's been some budget problems). I don't know everything that goes on of course, but my own job searches have turned up both interesting-looking embedded work and more run-of-the-mill web stuff, despite my earlier comment. I've seen lots of datacentre/hosting type companies kicking about as well.

It's no Silicon Valley - Wrexham, the population centre, isn't quite (though very nearly) big enough to hold the interest of the intellectually curious - but it's a lot more vibrant than you hear about. Here is the business directory of the business park in St Asaph where they're building the mirror segments:[2]

[1] http://www.glyndwrinnovations.co.uk/articles/latest_news/the... [2] http://www.stasaphbusinesspark.org.uk/directory/