I've read here some good things about the Cooler Master Hyper 212+ but it's only $30 compared to some Scythes at $45 -- is price an indicator of quality/noise, or is it because it's an older model?
The Hyper 212+ has just a very high performance/price ratio (see reference/recommended heatsinks on the relevant section of the website). The GELID Tranquillo should be another heatsink with such a good ratio, but I mean it's untested (by SPCR).
Scythes often (not always) excels in fans quality (and very often sports horrible mountings): this means that often you have to dial those Scythe fans down far less than other ones or they give more CFMs for the same rpm (in both cases you have more cooling power at similar same noise levels), or you won't be likely (or will be likely the less) to have a swap fan with them.
Just an example. If we give a look at these SPCR charts:
we can't do any apple-to-apple comparison, as SPCR changed its testing platform twice in the last months and these tables refers to different setups but, thanks to the third chart, we still may do some reasonable guessworks: as example, at the 12dBA level, a very comfortable one, the second table shows how the Cooler Master stock fan performs far worse than the reference (Nexus) one.
On the contrary, the Scythe stock fan (first table) is about on par with the very same reference (Nexus) fan.
So is the CM far worse than the Mugen? If we give a look at the third table, it's just 3-4°C under the Mugen, and not 10°C, using the same reference (Nexus) fan.
Therefore, if you are going to buy a separated fan (like a Nexus), you may go for the 212+ and still spare some bucks, for a slight worse performance (but quite acceptable!).
Otherwise, going for the Mugen will give you better out-of-the-box results, without buying any separate fan.
But if a 54°C rise is still acceptable with reference to your needs, you may go for the 212+ again, without buying any separate fan (and sparing a lot more).
Or you may want the best performance you can afford and go for a Mugen and a Nexus fan. And so on.
Just as a side note, both 212+ and Mugen Rev. B have a good mounting mechanism.
And forgive me if it's obvious and I missed it somewhere, but what's the general tool of choice for measuring system/component temperature?
Afaik, for an Intel system you may conveniently use either CoreTemp 0.99, or Open Hardware Monitor, and eventually SpeedFan.