Here's a list of the main sets available:
A List of Sidemount Regulator Sets
I'm hearing lots of good things said about the Deep6 regulators, but not yet had chance to return them out myself.
I've used Scubapro for decades and have been very happy with them. But sometimes I do wish I'd invested in Apeks across the board, as it'd make servicing and maintenance much easier.
+1 for this suggestion. I ended up selling all my reg sets and moving to XTX50 for my twinset regs, sidemount regs, and 2 deco regs. I did not purchase the kits however, I just buy the XTX50 first and seconds, then add my own rubber hoses and SPG. I love the large brass/glass SPG from Dive Gear express, and prefer rubber hoses to the Miflex type that come with the Apeks kits. Plus, I run two long hoses in sidemount, which is not an option with the Apeks sidemount kit. I did purchase the optional 5th port for the short hose reg on my twinset. Makes hose routing a little cleaner.