IMHO, compiler construction as an advanced excercise for amateurs is at topic that has been beaten to death (as OP suggests, there's tons of available materials and projects ranging from high quality not-so-amateur to quick or fun hacks - I'm guilty of one myself).
On the other hand, I would love to see "HTML5 and CSS parsing and rendering for amateurs". Given the state of modern HTML5 and CSS standards, and ignoring compatibility and real-world usage (just like for toy compilers), Let's Build A Browser Engine sounds more tempting than Let's Build a Compiler.
(To preempt "contribute to existing actual real-world engine" suggestions -- while that's worthwhile, it's like saying "contribute to LLVM" to someone looking to write a toy compiler, ie. completely misses the point).
On the other hand, I would love to see "HTML5 and CSS parsing and rendering for amateurs". Given the state of modern HTML5 and CSS standards, and ignoring compatibility and real-world usage (just like for toy compilers), Let's Build A Browser Engine sounds more tempting than Let's Build a Compiler.
(To preempt "contribute to existing actual real-world engine" suggestions -- while that's worthwhile, it's like saying "contribute to LLVM" to someone looking to write a toy compiler, ie. completely misses the point).