For vfm? 45-55mm
They’re all really expensive compared to 31.8 which is a bit annoying.
Raceface aeffect sometimes come up for a reasonable price on eBay - I splashed out and got a RF turbine on my fs bike which is really nice (but not vfm really).
On eBay there are some Kore and Onza stems for about £25 which I’m watching and toying with getting one of.
Nuke proof is 25 quid
I'd agree with @joebristol I love my Spank 35 vibrocores but in hindsight I should have gone with 31.8 esp as i'm using Direct Mount where the lack of choice/size is ridiculously limited and expensive
Tredz have a nice DMR Defy for £42 and you can get £5/£10 off regularly DMR
For functionality and looks, the nukeproof horizon stem is pretty impressive for £51 if you like your bits anodised,
The neutron is hard to beat though at £25.
Omikron stem from £15 at PX, but min length 90mm.