I find patients don't need to do this as often as they did ten or twenty years ago, mainly because so many inexpensive generic medications are now available. Also, some pills shouldn't be split because it disrupts a time release or protective coating or because their size or shape makes them difficult to split. If in doubt, check with your pharmacist.
Currently, one of the few tablets that my patients split is chlorthalidone. This is a less well known but often very effective thiazide diuretic usually used to treat hypertension. Generic chlorthalidone is quite inexpensive but doesn't come in a small dose tablet and many patients only need a half tablet daily for good blood pressure control.