Cinque Terre alternatives?
 

Planning 3 nights in Cinque Terre in October but getting a bit nervous after hearing how touristy/crowded it can be. Any suggestions for an alternative in the northern part of the country (we'll be coming from southern Tuscany and continuing on to Florence afterwards) that would also offer good hiking and scenery? Something else on the Italian Riviera or Le Marche perhaps? Would prefer seaside villages like CT but not necessary.

I wouldn't be as concerned about crowds in October as I would about the weather. The hiking trails can be a bit slippery and hard to navigate if there has been a lot of rain and some might even be closed. Early October would be your best bet. We have visited towns on the Italian Riviera and done a lot of walking, but not hiking. Cinque Terre is worth a visit but, IMO, only if you plan to hike. Not much else to do there although we had good food.

Yes, early October is a great time to visit the CT. I have visited twice, once in early October when I was lucky to have excellent warm weather. (Glad I brought shorts to hike!) On my last visit in 2011 (mid-September) it was very crowded, but I still enjoyed returning and hope to go back again someday. And I don't like overly-touristed places generally. For me, the CT was still worth it. I doubt I'd go in the summer though!

Montemarcello national park: Lerici is a great town and Tellaro quite beautifully situated.
The north side of Portofino national park also quite nice (not a fan of Portofino the town).
The Maremma of southern Tuscan coast was a strong contender for my vacation this year, but Croatia won out.
There are some trip reports about Le March you may wish to peruse.

http://liguriah.wordpress.com/2012/01/01/hike-index/

I took the hike listed to Portovenere in late August: it was excellent and we had the trail almost to ourselves.

I didn't experience many crowds in October either, but I did experience some terrible weather. I was fortunate to get my hikes in before/after storms.