How much XP do Rare monsters and Champions give?

Relative to their base experience Blue Champion demons will give 3x the amount of experience of their normal counterparts, White demons in Yellow Champion packs will grant normal experience, Yellow Champion demons will grant 5x the amount of experience as normal. Any illusions summoned by these champions offer no extra experience.

The linked infographic gives a good outline of how much exp is given for each monster kill throughout all acts on inferno.

http://i1007.photobucket.com/albums/af193/Loignite/ExperienceGraph-1.png

Whilst it may be tempting to skim around these monsters, it is always advisable to turn down the MP if you're having problems, remember there's a higher chance to drop on items from all champion monsters.