Well if you have an old dimmer system, you can't use the new CFLs, so trying to find the best PAR38 light bulbs. There aren't many good review sites, so here is a summary. Right now you have a choice of a few technologies:

• Incandescent. The original, cheapest but last the last
• Halogen. More efficient and last long. About $5 a bulb • CFL. If you don't have a dimmer, this is the one for you. • LED. These are supposed to last years and years, personally, I've had bunches of early failures with them, so maybe not worth the$40 a bulb

When you pick them, try to get the lowest wattage you can stand, usually 75-90 watts and the 130 volt ones last much longer (5000 hours vs 2500 typically), so that essentially halves their cost.
Other issue is the beam width, there is spot, flood and wide flood. Flood is the normal case.
Besides home depot, I've also ordered from 1000bulbs.com, so we see how they do with the Sylvania 14577 90 watt, 5000 hour, flood for about \$5 each.