Getting out the checkbook, eh? I find the most useful instrument is actually the binnacle compass. We use it to track lifts and headers, find the marks, plot rhumblines, gauge the angles on the competition to see if we''re gaining or losing and to determine if we''re making someone or will have to duck them. (We also have a digital compass which is only useful for some of those functions.) Secondly, the speedometer, finely calibrated, tells us if a trim adjustment makes a difference. The GPS would proably come next, helping to set courses to marks that are out of sight and letting us know how the current is setting us. The depth gauge lets us know if we are brave or stupid to be cutting so close inshore, and so is perhaps more valuable than it might at first appear. Lastly, the Apparent Wind Indicator can be really nice. This is especially so at night, when the telltales aren''t easy to see and you don''t want to announce yourself to the competition by shining a flashlight on your sails. The AWI is also good for telling you when jybing might be advantageous, particularly in light air when it''s blowing a little harder and from a little diffent direction at the top of the mast. We also have a SailComp, but in four years haven''t really figured out how to best use it yet - the previous owners lost the manual. Hope this is helpful, and (perhaps) lets you save some money for that sail...