For a nice custom board like the GON, I would look for something from a Group Buy. It's a bit of a sacrilege to put caps on that board that aren't truly great.
If you like green, then this one may suit you:
http://www.pimpmykeyboard.com/deals/nuclear-data-green-old-skool-sa-row-3-keycaps/Here is the relevant GeekHack thread:
http://geekhack.org/index.php?topic=61198.0It's SA profile, which is a tall profile with "spherical" indentations, like some old terminal keyboards, thick doubleshot keycaps. ABS material, but nice caps and you can fill out a TKL with just the base set.
Here's another green set:
http://geekhack.org/index.php?topic=60797.0If you're looking for something a little more classic and understated, I would ask in Ivan's GMK Dolch thread if someone is willing to transfer their set to you, or wait till it ends and check for them in Classifieds. GMK Dolch is Cherry profile, thick doubleshot ABS.
I believe Ctrl Alt Store (Bunnylake, codyeatworld and MargoBaggins) may start a run of GMK HyperFuse sometime soonish. That would be a very nice set, too. It would look like the DCS version shown here, but Cherry profile made by GMK:
http://geekhack.org/index.php?topic=48514.0In terms of thick PBT, there are some nice sets around, the best are dyesubbed, dark legends on lighter coloured caps. IMSTO sells some of the best quality ones, but he has limited colours available. See the blue and grey sets here:
http://imsto.cn/index.php?route=product/category&path=62Keycap profiles are a personal thing, but so far I like Cherry profile the most, followed by DCS (but the bottom 2 rows are a bit too steeply angled). I am hoping to try contoured SA profile soon, but it's very rare at the moment (although Matt3o is in discussion with SP about making the right molds for the Midnight SA and Retro SA Group Buys... here's hoping). I don't mind "flat" profiles like DSA, but definitely prefer contoured.
Browse the Interest Checks and Group Buys sections of the site. You may find a set (or 2, or 3) that calls your name