I do like to tinker with Sinclair BASIC every so often, here's 3 things I've made over the last 3 years.
Who doesn't like drawing with character blocks? I'll be honest I can't remember which algorithm is employed here, but it's a nice effect all the same.
This one is a good one if you're a fan of typing in many many DATA statements - something I didn't do (thank you ZX Editor!). Simply change the string on line 10 and run the program.
Wanting more chunky goodness I had a go with Bresenham's circle drawing algorithm.