What do people recommend for getting started with data visualization in clj/cljs? I just want to do some simple plots and graphs. I would prefer clj to cljs, but either is fine.

For genuinely simple stuff, I would just spend some time building a framework in Quil or just SVG in whatever web framework you're in. Oz has nice output and if you're already web based its fine. I find it a shame there's not something more agnostic, and also I genuinely think with the full power of Lisp you can probably do better long term than these largely declarative Grammar of Graphics derivatives, but haven't prodded too deeply. If you have ongoing complex needs in the future, it's a safe bet to work out how to use d3 in ClojureScript, that's a huge ecosystem.