Jungling 3v3 is possible and is seen in higher ELO games. There are lots of videos showing it on own3Dtv. I recommend browsing Twisted Treeline videos to see how it's done.
Good junglers for 5v5 also are good junglers for 3v3, but keep the differences between 3s and 5s in mind. In addition to aggressive dps champs being favored in 3v3, there is more competition for the small number of camps in the jungle. Aggressive junglers do well because they have plenty of opportunities to harass the enemy; Nunu and Cho Gath come to mind, both being strong junglers with good ganking potential and great harassment. If you watch some Twisted Treeline games you will see non-aggressive junglers like Warwick being dominated.
For Summoner's Rift (5v5)
Baron Nashor - 15:00 initial, 7:00 respawn after death
Dragon - 2:30 initial, 6:00 respawn after death
Lizard/Golem - 1:55 initial, 5:00 respawn after entire camp death
Wolf camp - 1:40 initial, 1:00 respawn after entire camp death
Wraith camp - 1:40 initial, 0:50 respawn after entire camp death
Small golem camp - 1:40 initial, 1:00 respawn after entire camp death
For Twisted Treeline (3v3)
Ebonmaw (Dragon) Buff - 4:40 initial, 5:00 respawn
Grez (Lizard) Buff - 2:10 initial, 4:00 respawn
Ghast/Rabid Wolf Buff - 1:55 initial, 3:00 respawn after entire camp death
All small camps - 1:40 initial, 1:15 respawn after entire camp death
Not sure if these values are 100% accurate for Twisted Treeline after the recent jungle remake. If anyone has specific info, feel free to comment/edit it in.
Special Notes:
The values listed for the Ghast/Rabid Wolf and Lizard/Golem initial spawn are 1:55 officially in the wiki, however this appears to vary by about 1s and in practice they're actually a bit closer to 1:54 on the in-game clock
As indicated, a camp of neutrals will not respawn if even one mob is left alive in that particular camp. The timer to respawn will not start until the last mob is killed. For example, if I kill the Blue Golem at exactly 3:00 but leave the small casters alive, the Blue Golem will not respawn at 8:00, but rather, 5:00 after whenever those two casters are killed.
Also, unlike HoN / DotA, neutral mobs will still respawn if there is something obstructing their spawn point (e.g. a ward, an object like Shaco's JitB or a Nidalee trap, a player, etc.)
Best Answer
I played custom game to see what is true.
(Do note: These pictures are outdated. Bonus gold is now +3 )
You get 3 gold per kill and 10% buff to AD and AP.
Also, every time you capture an altar, you gain 80 gold per player, 240 gold total for the whole team. This means capturing both altars will net your entire team 480 gold.