I think most, if not all, of the major reputable production knife companies have limited lifetime warranties. That said, though, there are still some that stand apart from the others. Namely, they'll go to greater lengths to make sure you are taken care, even if what you are asking falls outside the strict scope of the warranty policy.
Two that I think stand above the rest are KAI (Kershaw / Zero Tolerance) and Leatherman. KAI's customer service is responsive and very accommodating. They're also one of the few (if not only) that won't void your warranty if you disassemble your knife (cleaning/maintenance and such). In addition, they'll even send small replacement parts (screws, torsion bar, pocket clip, etc.) for their factory blems, which explicitly carry no warranty. As for Leatherman, their warranty seems to be if you can break it, they'll replace it, no questions asked.