favourites with my marshalls:
thundertomate phil hilborne treble boost - amazing for single coils and vintage output humbuckers, not so good for anything else
mi audio crunch box - it has multi uses really, nice with bad amps and brighter sounding pickups - ceramics, fender coils etc
rc booster - really awesome booster, 2 band eq is nicely designed. its not quite what i want, but hard to describe how i would change it. the ac or bb models might be better for me, but i won't be taking a risk selling this without trying first
modded boss ge7 eq - great pedal, love using it as a booster, very low noise
korg pitch black tuner - nice and accurate, plus easy to use
live:
modded boss cs-3 compressor - it was pretty rubbish as stock, highly useable in modded form, gives back a bit of valve like sustain
sansamp gt2 - indespensible really
korg pitch black also
also good:
modded soundtank tubescreamer - i don't use it often, but it has the typical tubescreamer tone
arion stage tuner - cheap and reliable