I have many, many white, red and black dice from
GW that I use in general for mass rolling. That said, I only use dice of a single colour per faction I'm playing. As I largely solo-game, this allows me to have many multi-faction battles with large amounts of dice being rolled.
I have a few random larger dice from board games and such, and I use the black red and white ones to bolster the numbers of the above mass rolls, although I don't really like it. Somebody posted earlier that larger dice and small dice in the same roll don't feel right, and
imho they aren't wrong. A couple of blue dice I have from the board games I use for things like magic and psychic powers, because blue is obviously the colour of magic
My 5 green dice from the Mantic
KoW starter box are my lucky important dice. I can't say whether they actually roll any better, because I'm naturally bad at rolling dice anyway! I think I need to try a new technique or something.
And finally, my free dice I got from the Salute 2013 event has a Greek Hoplite Helm and the inscription 'SALUTE' upon the '6' facing. I haven't used it in a proper game yet, but seeing as in a little game I played earlier, the Hoplite Helm came up a fair amount, I'm going to have that one as my duel dice for when things hang in the balance
Then again, a lot of things also affect my performance. If it's sunny I tend to play better (or at least ignore bad results more), and if a good bit of music is on, my dice appear to be more complacent