New Chemical Data Search Engine

[Rhodium]

Check this out - this is the best free online resource I've seen since chemfinder.com came online:

http://www.chemexper.com/

[Kinetic]

Chemexper is one of my favourite sites - I didn't want to post it because I wasn't sure whether it was a 'source' (it only has a few chemical companies listed). The search by substructure is excellent - also try searching for '3,4-methylenedioxy' and click on 'show structures' for 59 interesting precursors