Amazing site offers free service to find the cheapest mobile package which is most suited to your usage pattern.
Other than the usual minutes and texts, includes analysing data packages, picture msg, international calls/texts and roaming (even by geography!).
Can be limited to specific mobile networks and contract lengths (or sim only deals) but this is found only on the second page after you conduct the initial search.
Well worth checking out if you are looking for a new deal! (or to see what you should be on). http://www.billmonitor.com