Online retailer and Intel Platinum Technology Partner Simply NUC offers a pretty nice selection of passively-cooled mini PCs. Ranging from low-powered Celeron up to i7 the diminutive systems are highly configurable (and Ubuntu-friendly).
Celeron Dual-Core Fanless NUC System (NUC4CLFYF) from $250
Celeron Dual-GbE Quad-Core Fanless NUC System from $332
Core i3 Fanless NUC System (NUC4i3WYFK) from $410
Core i7 Dual-GbE Fanless NUC System (NUC5i7RYF) from $710
