If you're planning to go in the big-enterprise space... the big one is Oracle Financials. Many companies use it to manage vendors, purchase sites, GL codes, buyers, approval levels, an item master, net payment terms, etc.

You guys are on the right track, but eventually you're going to hit a wall where you'll need some serious maturity with procure-to-pay.

I'm not sure how the tone of this comes across, or if it's in any way negative because you guys are onto something... but have a lot of competition that is often deeply integrated (see Service-Now catalogs for example).