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So, under EU ROHS I can't use under 85% or over 5% lead. Japan is nixing antimony, which is part of the 95/5 tin/antimony I was going to use instead.  I have heard silver plating...  Let's hear some other alternative solder types that might emerge as the new global 63/37 after all these new initiatives are in effect. 

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"A witty saying proves nothing."
-Voltaire

Check out the paper, "The Lead-Free Solder Alternatives Issue: A Defense Industry Perspectrive."  http://www.smta.org/files/smta_boston01_rafanelli.pdf 

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For every complex question there is a simple answer, and it is wrong.

The medical implant and defense industries are definitely concerned about the impact of lead-free alternatives. Both communities have tracked critical system failures to shorts created by tin whiskers. These caused a recall of at least one implantable device and several missile defense system test failures.

There is an active project within iNEMI to develop a standard for lead-free solder. They are looking for even non-members who have a desire to create this standard to join in their project.

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Vitreous Humor
"Eye can see clearly now..."

IPC has been performing a study of solder pastes to meet the requirements of RoHS. There appears to be a desire to create a common standard which can be demonstrated reliable. There appear to be advantages in sharing the standard when it comes to optimizing processes. The preliminary results indicate that there were 3 alloys of tin, silver and copper commonly used that were worth evaluating side by side. Testing resulted in no significant advantage to any one solder, but they did notice somewhat better resistance to cracking if the solder contained less silver. The preliminary conclusion was that SAC 305 (Sn / Ag 3.0% / 0.5% Cu) would be selected for standardization.

Does anyone have negative experiences with SAC 305?

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Vitreous Humor
"Eye can see clearly now..."

Silver plating has been around for some time, but most assembly operations do not handle the product correctly (tarnishing problems).  The pcb should be delivered in a sulfur free paper and vacummed sealed. 

Immersion tin is available and is very similiar to silver.  I'm not sure how well it has been working in assembly shops, but the tin will easily oxidize if stored for + 6 months before assembly.

An ENIG (electroless nickel and immersion gold) finish is the most popular alternative at this time.  Beware of pcb shops using a hard gold finish in place of ENIG, components will actually fall off the boards after assembly if the wrong finish is applied and it can be very difficult to detect the difference.

Nickel/Gold finishes will maintain thier solderability much longer than silver & tin finishes.

There is also a Hot Level Tin finish similiar to the HASL , but requires a higher temperature which eliminates FR4 laminate so you must use something like a phenolic based laminate.  Very few places offering this finish.