I installed the BitMo Tri Mod on my EVJ combo & have been really impressed with the results.
The 2 stage gain switch it adds (as well as a very useful tone knob) means I don't have to put an overdrive pedal in front of it to get a real rock crunch. I'd never soldered before doing this so am very surprised it works. Drilling the amp was a bit hairy though!
But it is still damn loud. There's a UK based guy on EBay that's selling a pentiode/triode switch to get the amp down to 2 watts. He also sells a standby switch, HT fuse & line out mod. I'll probably get that next.
BM
a lot of these mods you can basically get for free from that 18 watt thread- obviously you have to buy the parts. But I suspect it's cheaper to buy the parts.
also, what the 18 watt thread gives you is a discussion on the relative merits of various part swaps, how to voice your amp to what you want, etc.
I'm not trying to complain about these kits or anything, but a lot of these mods seem to be pretty simple, i think the parts for the "gold" mods are something like $10 (excluding the upgraded OT, which these kits don't include anyway). EDIT: and according to that thread (and I believe them, it makes sense) the OT is the one best component swap you can do.