The number of leads your website generates for your business is a function of two things; 1) How many relevant visitors are you attracting to your website, and 2) How many of them are converting?
If your monthly traffic levels are less than 50,000 unique visitors, I suggest you focus your efforts on increasing the number of relevant visitors.
For help in how you do this, take Inbound Marketing University, from BillBelew.com.
On the other hand, if you're website is already attracting 50,000 plus unique visitors a month (preferably 100,000 plus) you will do yourself a favor to take a look at WiderFunnel.com.
A brief conversion with their CEO (Chris Goward), assured me they know what they're doing.
WiderFunnel does not "drive" traffic (which is a bad metaphor anyway - you want to attract relevant traffic).
Their focus is effectively communicating value and removing user experience issues. Conversion is truly one of those areas where "less is more". That fact that he gets this is important.
Their expertise is in marketing persuasion, removing conversion barriers, and testing.
To get a feel for what they're about, you can also check out Mr. Goward's book titled "You should test that" available at Amazon.com.
If your website has 50,000 monthly unique visitors, with a 1% conversion rate and a $100 average sale (very conservative numbers were chosen intentionally), a conversion rate increase of only one additional percent is an extra $50K a month in revenue. Definitely worth investigating.
You should check these guys out.