I have a Uniden booster that I got from these people-
http://cellularbooster.com/
Where I live, we had a weak signal, and dropped calls constantly inside the house. I called them, and they locate where the towers are relative to you, and ask you some questions about geography in the area, etc, then give you some options as to boosters and antennas. There is a unidirectional antenna outside, on the roof, that points to the local cell tower, an amplifier inside the house, and a small antenna inside the house.
It works VERY well. I use two different cell providers (Work phone and personal), and my Verizon signal went from weak 1-2 bars and frequent dropped calls to full 5 bars and never a drop. My AT&T went from no signal to 2-3 bars.
It was a bit pricey ($300-$400 range, I think), but does what I need it to. Might be overkill for what you need, though.
Oh- One more thing- I was able to get the cell phone company to 'help' with the purchase, since the signal was so bad in my area even though the coverage map showed it was good. The only option they could offer was a repeater that hooked up to my internet service, which is NOT an option for me since I'm on Satellite internet and can't use that kind of bandwidth. They gave me 2 $80 bill credits to help out. It doesn't hurt to ask- Especially if you are nice about it!
-Andrew