Resources

Need to Know facts

The Knowledge for Year 13 - final version - and The Knowledge Answers to check.
The Knowledge for Year 12 - updated for February half term - and The Knowledge Answers to check.

Topic Specific Resources

If you know you have some weak topics then you should target these first, rather than jumping straight into full past papers.

If you want to practice past paper questions on a specific topic then ALevelMathsRevision.com is a great website - they have resources for both Single Maths and Further Maths that are selected to be suitable for the new specification. Each sheet has accompanying mark scheme solutions.
Integral Maths is an obvious option and has not only worksheets with full solutions but also video explanations to help recap topics that are causing more problems.
The Edexcel Textbooks have been uploaded in pdf form by someone on Reddit to this Google Drive. The Single Maths books have a 98% overlap with our specification. The Further Maths books don't match as perfectly but will still be great for extra questions on some topics.
MadAsMaths - the "Maths Booklets" section has excellent, challenging topic-specific questions with full written solutions. It can be a little difficult to navigate so go here for integration, here for trigonometry, and here for other Single Pure topics. For Futher Pure topics you can find sheets on complex numbers, roots of polynomials and special sums here.
Physics and Maths Tutor also has topic specific pages with cheat sheets as well as selected questions.

Videos

You can find quick videos on a few of the topics on my Youtube channel - if you go to the playlists they are organised by paper.

There are also incredible videos by TL Maths - these cover every single topic from both Single Maths and Further Core Pure, Mech Minor and Stats Minor. He has a Youtube channel but the videos on his website are amazingly organised and easy to navigate.