Asides from Ursa, some of the better heroes for soloing Roshan from levels 6-10 are:
Enigma: Using Eidolons and a Medallion of Courage. You may also need a Soul Ring to keep your mana pool up. The idea here is to cast cast Medallion on him to reduce his armor to greatly increase your Eidolons' DPS. As MadCom mentions below, Medallion doesn't proc Roshan's spell shield so you don't have to worry about him blocking it.
Venomancer: Using Plague Wards. Create a wall of wards between you and Roshan and you should be able to right click him to death.
Lycan: Using his wolves and a Vladimir's Offering. Shift aggro appropriately to tank damage.
Lone Druid: Using his bear and a Vladimir's Offering. Shift aggro appropriately to tank damage.
Troll Warlord: With points into Fervor and Battle Trance and either Vladimir's Offering or a Helm of the Dominator. It's also recommended you switch into melee form for faster attack speed, health, and damage (also, Vladimir's Offering wouldn't work if you were in ranged form anyways).