For electric:

I just bought 10 packs of .010 to .052 (10-52's) from eBay for $65 + $15 shipping, and it saved me about $100. They are GHS Boomers and they sound awesome! Best thing I have done for my guitar playing in a little while because now as soon as I can hear the strings are getting dull, I can change them out immediately without having to wait till I have the time to go and buy some. I wouldn't recommend buying in bulk until you have an idea of what type and gauge you want of course.. but when you do find your favourites, it makes a lot of sense.

I usually recommend 9-49's to people who ask me, they are quite light and still have a decent sound.

My acoustic strung with Dean Markley - PhosBronze - XL 10-48's, they don't stay very bright for long but they are durable and have a nice action. I'd recommend these over the LT's which are 11-42's because it has a nice transition of light through to heavy. The LT's are good though because they keep everything light throughout all 6 strings.