A couple of good websites to check out the latest interest rate deals are:
www.moneysupermarket.com
www.moneysavingexpert.com
Deals offered by banks and building societies are continually changing and offers often don't stay available for very long so you need to start checking around a couple of weeks before your fixed rate bond (or whatever it is) matures. Also, if you're a taxpayer, you may want to consider putting some of your maturing funds into a cash ISA - (After April you can put £5100 in a new Cash ISA every tax year) - so that you don't pay interest on your savings.