One of the issues with dining in Riyadh is the inconsistency - hence why it's difficult to get consistently good recommendations. Nevertheless my Lebanese colleagues swear by Al Reef, and I found the Globe to be overpriced rubbish (Entrecote is a better bet for eating at the Faisaliah Tower IMHO).

Najd Village is interesting in its own right, actually.

I'll second Cento per Cento, have eaten there way too often. Also in Olaya, the new Burger Boutique is fast becoming a favorite...

Other restaurants I am partial to: Tokyo on Ouroba St (sushi), Mama Noura on Thalatheen St (schwarma), Avadh on Tahlia St (Indian), Korean Palace on Makkah Road, and last but not least Lahori Khaabay in Hayi Al Wazaraat - their SAR 18 lunch buffet is a thing of beauty.

With regards to taxis - they will put the meter on if you ask (unlike in Jeddah!), though from the airport it can actually be cheaper not to.