The Samsung Galaxy Prevail is an entry level device for Boost Mobile. Unlike some of it's Galaxy S cousins, you wont find some of the higher end "Galaxy S" features and it doesn't have the familiar TouchWhiz interface seen on so many other Samsung devices.
The Prevail comes with an 800MHz single-core processor, 3.2-inch 320x480 capacitive display, a 2 megapixel rear camera, Wi-Fi, Bluetooth, GPS, and launched with Android 2.2 Froyo. Great value for the money.

The Samsung Galaxy Mini, is a smartphone manufactured by Samsung that runs the open source Android operating system. Announced and released by Samsung in spring of 2011. On the Indian market it is known as Samsung Galaxy Pop and on some other markets it is known as Samsung Galaxy Next. It is currently available in four different colors; steel grey, white, lime and orange. 

Features:
The Galaxy Mini is a 3.5G smartphone that offers quad-band GSM and announced with two-band HSDPA (900/2100 MHz) at 7.2 Mbit/s. The display is a 3.14-inch (80 mm) TFT LCD capacitive touchscreen of vertical QVGA (240x320) resolution. There is also a 3-megapixel camera, capable of recording videos at QVGA (320x240) resolution. The Galaxy Mini comes with a 1.2 Ah Li-ion battery. The Galaxy Mini runs on Android 2.2 Froyo.
Galaxy Mini is presented as a entry-level smartphone, and is (as of 13 May 2011) one of the cheapest Android phones around.
In May 2011, Samsung announced that the Galaxy Mini (along with other Galaxy models) will get an official upgrade to Android 2.3. As of November 2011 the rollout is still in progress. If voiding the warranty is not a concern then a leaked upgrade can be applied already.

#from http://en.wikipedia.org

The Samsung Galaxy Gio is a smartphone manufactured by Samsung operating the Android operating system.
It was announced at the 2011 Mobile World Congress as one of four Samsung low-end smartphones, along with the Galaxy Ace, Galaxy Fit and Galaxy mini.
In early August 2011, Samsung officially rolled out the Gingerbread update via Kies. In September 2011, Samsung rolled out an update in The Netherlands marked "PDA:KPS PHONE:KPA CSC:KP1 (XEN)" 

Features:
The device is equipped with a 3.2 inches (8.1 cm) HVGA screen, a three-megapixel camera and an 800 megahertz processor. It runs on Android 2.2, with Samsung's TouchWiz user interface.

#from http://en.wikipedia.org

The Samsung Galaxy Fit S5670 is a smartphone manufactured by Samsung that runs the open source Android operating system.
It was announced at the 2011 Mobile World Congress as one of four Samsung low-end smartphones, along with the Galaxy Ace, Galaxy Gio and Galaxy mini

Features:
The device's is equipped with a 3.3 inches (8.4 cm) QVGA screen, a 5-megapixel camera and a 600 megahertz processor. The Fit runs on Android 2.2 Froyo and a modified version of TouchWiz, Samsung's proprietary user interface. The Galaxy Fit also has a Swype option which allows you to draw lines from letter to letter in order to type.

#from http://en.wikipedia.org

The Samsung Galaxy Ace, is a smartphone manufactured by Samsung that runs the open source Android operating system. Announced and released by Samsung in February 2011, the Galaxy Ace is the successor to the Galaxy 3.
The Galaxy Ace is one of the four budget, low-cost Android-based smartphones planned by Samsung. Being an upper mid-range smartphone, the Ace has a hardware between that of the Galaxy 3 and the Galaxy S; it features an 800 MHz Qualcomm MSM7227 processor with the Adreno 200 GPU.
It is currently available in black with back covers in two different colors, black and white.
Features:
The Galaxy Ace is a 3.5G smartphone, offers quad-band GSM and announced with two-band HSDPA (900/2100) at 7.2Mbps. The display is a 3.5 inch TFT LCD capacitive touchscreen of HVGA (320x480) resolution. There is also a 5-megapixel camera with LED flash, capable of recording videos at QVGA (320x240) resolution and VGA (640x480) resolution with the Gingerbread update. The Ace comes with a 1350mAh Li-Ion battery.^[7] The Ace runs Android 2.2 Froyo, Samsung's proprietary user interface and is also upgradable to Android 2.3.5 Gingerbread.
Ace has heavy social network integration abilities and multimedia features. It also is preloaded with Google Trademark Mobile Apps.

#from http://en.wikipedia.org