Many people come to this site looking for an online lead generation form. The fact is, your HTML web form for lead capture will be very different depending on what kind of online lead capture you are doing.
For example, I use some free tools for sites that do not get many requests and require manual follow up such as speaking leads. For that I either use InfoDome or Google Docs to capture leads.
You might wonder why not a lead generation wordpress plugin. The fact is, there are a lot of contact us plugins and web form plugins but I have had mixed results with them. Every time there is a wordpress upgrade or a plugin upgrade it might stop working and you may not realize it.
Next I use aWeber for building email lists and capturing online leads where I want to automate the followup. Very good and affordable tool for online lead generation form building that is simple and effective.
Lastly you can use full CRM systems to build your lead generation form. Tools such as Zoho CRM and SalesForce.com have these tools built into them. I tried using vTiger open source crm and did not have luck although maybe by now they have made it easier.
The key is that there are low cost and higher cost systems for adding online lead generation forms to your WordPress lead generation site but you want to chose one you can count on and also test it often.