Swiftech do a nice 90 degree articulated fitting. It has a male thread on one end to attach onto a rad or other component in your loop. i.e reservoir, gpu block etc, and a female thread at the other end where you can attach another fitting to it.
They are't cheap but the sure do look nice.
http://www.aquatuning.co.uk/water-cooling/fittings/adapters/14796/swiftech-angled-adaptor-90-dual-revolvable-g1/4-inner-thread-to-g1/4-outer-thread-lok-seal-black?c=2662