Here’s a Marshall Amplifier I’ve created. It took me a few hours to create, though I’m not sure how many exactly. I’m trying to make it look as realistic as possible, so any criticism on that would be great!
Hi res: http://1.bp.blogspot.com/_vfkyomEnc-E/TIQkH1_PsnI/AAAAAAAAAQM/FQZ2L0L3BMw/s1600/Marshall_amp.jpg.png
Great start, but here’s my… well couple of cents:
material settings, the gold needs to look like gold, it needs some sort of reflections. The marshall logo is plastic, a plastic material isn’t too hard to achieve. The outside needs a leathery normal map. and a little higher specularity
it looks like you have textured all the settings, but I’m really missing what kind of amp it is, as in, mine said MG100HDFX… what model is it?
to make it realistic, you should model at least the "speaker"part behind the grill, I know for a fact that it always shows through, not much, but it does.
The on/off button is usually either black or red semi-seethrough plastic with a light behind it.
That’s about it for now, but I’m sure you’d thought about all of that anyway. Damn I miss my Marshall.
EDIT: OH, I’m missing the dashes on the buttonthings, you know, which tell you the volume, gain, treble, bass, middle, reverb, etc.
saw this on your blog 
very cool…nice and sharp too
p.s. there seems to be a double *.jpg in the picture name, I just noticed…could potentially cause problems 
Looking good.
Couple things:
I’d say that the faceplate’s specularity might be a little harsh still. IIRC, the nameplates tend to have a brushed-look that reduces reflections and disperses the light a little more.
The leatherette, IMO, could stand to be a bit brighter and reflect more. It seems a bit dark for the given scene.
The dials look nice. Rotating them to realistic values will be a nice finishing touch. 
I would say that seeing a subtle outline of the speaker might be a nice touch, but the grill cloths for Marshalls tend to be pretty thick anyway. I think it’s fine as-is.
I’d like to see it from another angle.
I think you need to work on the lighting. On my screen it is very dark plus the angle of the shadow and the specularity off the front panel shows that the lamp is just in front of the Amp. In a real room it would be much higher up and spread much broader light. You may need to add/tweak the AO and Environment Lighting settings for realism
