Been a Pulse8 Broadband customer for 3 years now and I'm happy with the decision.
No frills, business-based provider that also cater for home customers.
Excellent customer service via phone or email.
No email included, so if your existing email is tied to your ISP, you'll need a separate account (if you're switching from Sky, you can keep your Sky/Yahoo email after you leave them).
Rolling 1 month contract.
Static or fixed IP options.
Broadband and phone package has reasonably priced call charges.
ADSL line speed can vary at times, but mostly stable and reliable. Connections aren't throttled.
Packages can be tailored with extras as needed.
Like most non big-name providers, if there's a fault with the line you'll have to pay the Openreach fees (although they offer a £1 pcm "Openreach Charge Assurance" option). So if you have issues with your line, get your current ISP to sort them out first.
Router isn't included, so you may need to factor in the cost of a decent router to the initial setup costs, if you don't have one (or the one you have is locked to your current ISP). Just make sure you get a router that supports the type of internet connection you're getting (i.e. fibre (VDSL) or standard (ADSL)). Pulse8 give you all the config info and tech support you need.
Not as cheap as over-subscribed big names, but competitive compared to top ISP prices.