I'm thinking about getting some new stainless brake lines and while I'm at it, rebuild/freshen up the calipers. If you've rebuilt a caliper before, what do you recommend? Has anyone used a rebuild kit? What pads do you prefer? I was digging around looking for recommendations, but didn't see any specifics.

SS lines are the best! An I've rebuilt my caliper it's just 2 orings per piston it's very easy. Just soak the new seals in brake fluid for a couple hours before you do and yeah straight foward procedure.

I personally do not bother rebuilding brake calipers. I buy nearly new, used calipers with nearly new pads for less than the cost of pads or a rebuild kit. I go for ones with <1000 miles whenever possible and from fairly new bikes, like 2007 or newer. Then I just pop them on the bike and I'm done. Bleed the lines. Takes about 5 minutes. No need to rebuild old calipers.
I just got in this for $9.95. also got the rear for $9.95 and the matching rotors for $24.95 each. The rotors were smooth as glass - virtually new.
New calipers fit old bikes just fine.
http://www.ebay.com/itm/200709358781?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

As long as I can pick up things like this for $10-$20, I see no need to rebuild old calipers. I've got a box I'm filling up with older calipers I'll never use again. Most are good but I prefer the newer parts.

Why rebuild when you can buy this for $10? I have a pile of SS lines so I replace the lines and fluid at the same time. If the bike is old, like 1992, then I buy a new, used master cylinder, too. And next time I do a rear, the rear brake switch will be replaced with a banjo bolt pressure switch.