i'm thinking about this one...
it's not lcd as i mistakingly wrote earlier just a two digit led readout. it's a self build kit... the only problem is that i don't have a convenient place to put it yet and the full assembly is fairly big. i've even been contemplating HUD like setups with a reflection in the window.... wich i doubt i could pull off, but still it would be cool :)

i suppose i'll have to check a car supply store to see what they've got... most sugestions listed above look good but i'd have to find alternatives available in europe