Apologies for using an thread title that may be considered inflammatory, just a light-hearted dig at certain members - you know who you are!
Hydrogenaudio.org is currently running a public listening test for 128kbps MP3. Samples from the latest versions of various popular encoders are tested against a reference uncompressed sample, and a "low anchor" sample encoded with the first ever public MP3 encoder (released back in 1994).
Link to the thread is here. By all accounts setting up the samples and test software sounds a bit fiddly, so if you fancy having a crack at this, make sure you read the included readme carefully.
I find this kind of test very interesting, so I'll probably have a go myself - although I expect with my ears I'll probably find it very difficult to reliably ABX any of the tested encoders.