Hero that can solo Roshan at an early level aside from Ursa
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.
Nature's Prophet: Using Treants and a Medallion of Courage. Use Sprout in the Roshan pit for trees to use. A Ring of Basilius will help your Treants tank Roshan more easily.
Shadow Shaman: Using Mass Serpent Wards. With careful placement of the wards by the edge of the Roshan pit, you can kite Roshan with your hero as the wards hit him.
Venomancer: Using Plague Wards. Like with Shadow Shaman's wards, kiting Roshan is the key. Plague Wards used to block Roshan so you could create a wall between him and Venomancer, but that is no longer the case.
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).
I agree drow can easily do rosh with lifesteal after level 6 but its risky and takes awhile. For pub games under 3k; Ursa can solo rosh at level 3 or 4 with 2 stout shields and a morbid mask. skill build should be 0 2 2. lvl 3 is risky as its dependent on how many bashes roshan gets but lvl 4 is guaranteed. Juggernaut can solo rosh after he gets a MOM and atleast 900hp with points going towards healing wards and crit. PA can do the same as Jug at lvl 9 with max blur and some kind of tanking/hp item like pms, 4 gauntlets etc. you could stop in between and salve up if rosh gets too many bashes. Hope this helps :)
Troll Warlord can solo roshan, just use and use his rampage.
Invoker is able to with 4 points into Quas and Exort for double forge spirits.
He has to have his units all split the damage taken.
Here is a video where the guy buys Helm of the Dominator.
And controls a 4th guy to tank it.
It's more efficient to buy a medallion for the - armor and 2 or 3 salves (tank with your hero until half health, then heal up while minions split damage) since Invoker doesn't hit hard enough for a Satanic to be worthwhile. Also medallion is usable on enemy heroes who die extremely fast then to forge spirit focus fire.
Try Drow. If you have a well equipped L8+ Drow, she can kite and kill Roshan. You need to rush in and start pelting Roshan with ice arrows (Drow's orb). When Roshan gets too close, back off and let it retreat. Then attack it again. Repeat till dead.