Any recommendations on where to stay in Santorini & Mikonos? I'm looking for beautiful views and relaxing few days...
Under $150 US dollars would be nice too.

Stay in the most beautiful village of Oia. Fira is too crowded and commercial. Try the Oia Mare Hotel, Perivolas Villas, Atlantis Villas. The views are spectacular.

Santorini-Hotel Keti was very nice. Right on the caldera with a great view but a steep climb (you can hire donkeys to carry your luggage back up). Anemomilos Hotel in Fira was terrible! Nice room but they were incredibly rude and you can find closer hotels to the caldera.
Mykonos- Hotel Carboni/Matoyianni is perfect of you want to be in the center of the town and plan on doing a lot of partying. The hotel is off a side dtreet so it is quiet and very clean.

I stayed at Dana Villas in Fira...it was around $120/nt for an efficiency (and that included the "finders fee" we paid the travel agency there). The villas are built into the side of a cliff, so some have boulders sticking out into the bedrooms! Each room has awesome views and an outdoor area for sitting. The villas share a nice pool also built into the side of the cliffs.

Check it out:

http://www.greekhotel.com/cyclades/s.../dana/home.htm

We spent four nights at La Perla Villas in Oia--I would stay there again without hesitation. Beautiful views, great pool, nice rooms--we paid $160 in July. Looked all around Oia, and for the money I really liked La Perla.