Rimmel Fix & Protect Primer - £6.99. I bought one about a month ago and it makes my makeup stay on longer than any others I've tried. There is a W7 one you can get on Amazon called Porefection that's supposed to be a good dupe for Benefit's Porefessional. I've not tried it but would like to. I've also got a Barry M one (Flawless Brightening Primer) that I like.
Mua range from Superdrug is brilliant. I use their wax primer or their cream one and both are brilliant. I'd spent £35 on a primer and foundation from boots no 7 and wasn't entirely happy with it for the price so I looked round and was recommended to try the Superdrug range. I bought two primers a foundation a bronzer and a hi lighter all for the same price of two items at boots. And it goes on smoother and stays on.