Dakka Dakka seems to have overtaken CoolMiniOrNot for me as a gallery showing off some great conversions. Take a look at these galleries.
The Burgomeister's Mansion Bell Tower is a phenomenal terrain project.
Jules le Jongler
Pirate Viking Painting has pictures up of one of Dreamforge's Leviathans painted up as in Imperial Colours.
And lastly, Eye of Error has used alt heads on his Dark Eldar Warriors to disturbing effect. The base work is also worth a look.