From Transum Software, the well known Maths Starter of the Day has just that, a starter for every day of the year. What makes the site particularly useful is the index by topic and note the link to Quick Starters, Random Starters and Substantial Starters. There is also a complete index of starters which includes the topic of the starter.
Many of the starters would make ideal Bell Work; there are several starters here which could be written up on the board whilst you are waiting for any IT – or maybe if you don’t have IT!
Some of the Shine and Write activities would also make good lesson starters. For example are these statements true, sometimes true or false? As with many of the activities on this site you can refresh the page for further statements, you can also change the level. Or perhaps some Mathanagrams?
Checking the National Curriculum (UK) section I came across this really useful mental calculations activity which you can refresh for a never ending supply of such questions. I then discovered the same activity in another format, using the topic index, under Mental Methods, we see that Know Your Place is one of the activities, this time a timer is included as are the answers. Further investigation of this section, led me to this rather nice starter on algebraic notation. As you can see each section has suggestions for activities, with additional suggestions such as the algebraic notation starter at the end of the section. This site is well indexed, from the algebra activity mentioned here, there is a link to other algebra activities
Well worth exploring for your favourites – this site is a rich source of starters and plenaries.