One great partner for Silas Renn is Bruse Tarl, Boorish Herder. Not only does Bruse Tarl allow you to also run Red and White cards, but his ability to give a target creature double strike means that you can get two activations out of Silas Renn, and not just one. Allowing a 4-color artifact deck opens up a lot of options. Red provides a lot of firepower and White provides tutor and recursion abilities, plus some White-only artifacts. This combination of colors makes for a deck that can set up its win conditions in new and exciting ways.
The other Partner Commander that seems to fit well with Silas Renn is Vial Smasher the Fierce. Not only does he bring Red mana to the deck, but Vial Smasher's ability can really wear opponent's down while you get your board set up. With the Goblin Berserker on board, when you cast your first spell each turn, he deals damage equal to that card's converted mana cost to a random opponent. This makes for a non-political way of doing damage without having to actually attack. It probably won't make you very popular, though, but blue and black have plenty of ways to stop opponents from attacking or greatly disincentive them from doing so
While Silas Renn's ability appears pretty fair on its own, him being able to Partner up opens up the number of cheap things he can allow you to recast. That's really where you want to be with a Silas Renn deck, consistently recasting cheap artifacts with sacrifice abilities. You will want to make him unable to be targeted by opponent's spells (hexproof) and make him unable to be blocked so that he can connect on a regular basis. Incremental card advantage adds up over a long game and typically the player with the most options has the best chance of winning the game. This guy is going to be fun to build arround and I can see him having a place in the 99 of many other Commander decks, as well.