If you want/need a Blackberry, you will know about it.
As you don't (I wouldn't buy a Blackberry as a media/general use phone), and want around a ?30 per month contract, look at the Samsung Galaxy S or HTC Desire.
You can get the iPhone 4 on a ?30 per month contract but you need around ?260 up front for the phone (32GB anyway)
Its very, very easy getting a contract phone online, go and look here -
http://www.mobiles.co.uk/
http://www.mobilephonesdirect.co.uk/
Both the above websites are decent and will give you a good indication of prices.
?30 per month will EASILY get you a top end phone