Many times we want to check android browser behaviour for particular site on desktop. There is no common user agent string for android browser across all the android vendors like Samsung, Motorola, HTC, Sony Ericsson and Dell. Please check my tutorials to change the user agent on Chrome and Firefox.
This list will help you to choose the right user agent string for your target.

Google Nexus

Google Nexus User agent(Build/FRF91)

Mozilla/5.0 (Linux; U; Android 2.2; en-us; Nexus One Build/FRF91) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

Google Nexus User agent(Build/ERD62)

Mozilla/5.0 (Linux; U; Android 2.1; en-us; Nexus One Build/ERD62) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/530.17

Motorola

Motorola DROID 2 User agent

Mozilla/5.0 (Linux; U; Android 2.2; en-us; DROID2 GLOBAL Build/S273) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

Motorola XOOM User agent

Mozilla/5.0 (Linux; U; Android 3.0; en-us; Xoom Build/HRI39) AppleWebKit/534.13 (KHTML, like Gecko) Version/4.0 Safari/534.13

Motorola DROID User agent(Build/FRG22D)

Mozilla/5.0 (Linux; U; Android 2.2; en-us; Droid Build/FRG22D) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

Motorola DROIDX User agent

Mozilla/5.0 (Linux; U; Android 2.1-update1; en-us; DROIDX Build/VZW) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/530.17 480X854 motorola DROIDX

Motorola DROID Build/ESE81 User agent

Mozilla/5.0 (Linux; U; Android 2.1-update1; en-us; Droid Build/ESE81) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/530.17

Motorola DROID Build/ESD20 User agent

Mozilla/5.0 (Linux; U; Android 2.0; en-us; Droid Build/ESD20) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/ 530.17

HTC

HTC Desire User agent

Mozilla/5.0 (Linux; U; Android 2.1-update1; de-de; HTC Desire 1.19.161.5 Build/ERE27) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/530.17

HTC Droid Incredible User agent

Mozilla/5.0 (Linux; U; Android 2.1-update1; en-us; ADR6300 Build/ERE27) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/530.17

HTC WOWMobile myTouch User agent

Mozilla/5.0 (Linux; U; Android 1.6; en-us; WOWMobile myTouch 3G Build/unknown) AppleWebKit/528.5+ (KHTML, like Gecko) Version/3.1.2 Mobile Safari/525.20.1

HTC Desire User agent

Mozilla/5.0 (Linux; U; Android 2.2; nl-nl; Desire_A8181 Build/FRF91) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

HTC Cupcacke User agent

HTC_Dream Mozilla/5.0 (Linux; U; Android 1.5; en-ca; Build/CUPCAKE) AppleWebKit/528.5+ (KHTML, like Gecko) Version/3.1.2 Mobile Safari/525.20.1

Samsung

Samsung Galaxy Tab User agent

Mozilla/5.0 (Linux; U; Android 2.2; en-gb; GT-P1000 Build/FROYO) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

Samsung Galaxy S User agent

Mozilla/5.0 (Linux; U; Android 2.2; en-ca; SGH-T959D Build/FROYO) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1

SonyEricsson

SonyEricsson x10 mini/E10i User agent

Mozilla/5.0 (Linux; U; Android 2.1-update1; de-de; E10i Build/2.0.2.A.0.24) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/530.17

SonyEricsson X10i User agent

Mozilla/5.0 (Linux; U; Android 1.6; en-us; SonyEricssonX10i Build/R1AA044) AppleWebKit/528.5+ (KHTML, like Gecko) Version/3.1.2 Mobile Safari/525.20.1

Dell

Dell Streak User agent

Mozilla/5.0 (Linux; U; Android 1.6; en-gb; Dell Streak Build/Donut AppleWebKit/528.5+ (KHTML, like Gecko) Version/3.1.2 Mobile Safari/ 525.20.1