Here are resources outside of this site that will be helpful for use of UTAU. Many of these are linked within tutorial pages.
UTAU (Windows) most recent version – v.04.18e
UTAU-Synth (Mac) most recent version – 1.0.0 b20 (under UTAU-Synth for MacOSX)
Bizz’s “The Best Things I Could Think of, Etc” Plguin aka Iroiro – iroiro2.zip is most recent version and has a ENG interface! This tutorial guides you how to change the interface language. (You only need to download iroiro2.zip. The tutorial was made for an earlier version that required a separate language patch.)
BGM Player – useful for playing the instrumental of a song or playing two or more USTs at a time
Resamplers are often difficult to find and link to, because the sites they are hosted on go down or do not show up in search results. Here is a mirror containing several resamplers - EFB-GT, fresamp (versions 11 & 14), moresampler (0.8.3 & 0.8.4), TIPS, and tn_fnds.
I would recommend putting the resamplers in the UTAU directory wherever you installed UTAU - I keep a folder named "resamplers" to hold all of mine. Do not move or change any of the docs in moresampler or tn_fnds, as they need those to run.
To change the active resampler, in UTAU, go to Project > Project Property and click the button with three dots (...) at the very right of "Tool 2 (resample)" and replace it with your resampler of choice (Moresampler needs to be in both Tool 1 and Tool 2). Some resamplers will not work well with certain UTAU voicebanks; some will not run at all, some will only render garbled noise.
utau.wiki – a comprehensive database of UTAU voicebanks
utau.wiki – filtered by Voicebank Style
utau.wiki – filtered by UTAU name
Setting Locale to Japanese for Win7/Vista/XP
*Please note: As of fairly recently, Audacity versions 3.0.3 and newer have some form of telemetry and strange data privacy concerns. I'm not aware of the current status, but for now, I'm linking to a mirror of older versions of Audacity. I highly recommend you download v3.0.2 or v.2.4.2 at this time.