A Friend and I are going to Spain in early October, and have 8 days and nights. We are flying into Barcelona and out of Madrid, but have not mapped out the trip. How long should we spend in Barcelona and Madrid? What other excursions would you recommend outside the cities?
Thanks

If you have only 8 days for everything..I would go for 4 days in Barcelona and 4 days in Madrid (or 3 and 5). You don't tell from where do you come, but if you come from the US you will probably almost "lose" a day with jetlag so you will have only 2 or 3 days in Barcelona, which should be enough but no time for day trips.
In Madrid you can do a day trip to Toledo or Segovia, both deserve the effort

Another Question: if doing a day trip outside of Barcelona is Montserrat or going up the Costa Brava the best bet? Looking to be active, but also enjoy the ocean views. What are the beaches like in early October?

I would look at it a bit differently.

Check with Iberia. If you can get a really cheap (20-35E) flight from Barcelona to Seville, consider 3 days in Barcelona, 3 in Seville and then 2 in Madrid.

Probably a bad idea but Seville....

I think Myer has a good idea, if you can get the flights at the good rate. Also, I'd suggest making a daytrip from Madrid--either Segovia or Toledo would be a great day trip.

You can have a good enough day to go to the beach..but that's not the norm in October
As a day trip, Montserrat is a better bet. It's nearer from Barcelona than Costa Brava. Another option for a day trip is Figueras to visit Dali Museum, which is a great visit

Back to Seville.

If you feel you have enough time for daytrips, then definitely skip them and get to Seville.

You won't be sorry!!