If a new web site becomes too popular too soon, it can suffer from the thundering herd problem. To slow the stream of new users, many institute an invite program, where users need an invite code to sign up.

Knowing how to get an invite can be eminently useful. Why, you ask? To register your preferred username, get in on early bird treats (sites often give out perks to encourage early adopters) or to try out a new site before everyone else. For example, I got 5GB of free storage at DropBox while later users only get 2GB free (it’s still a fantastic service). Another example is that I’m enjoying my Grandcentral (or Google Voice) account while others are still waiting for invites. If you enjoy trying out new sites, getting beta invites is the only way to go.

Where do you get an invite? I’m glad you asked. I’m an invite aficionado. I got an invite to Gmail in mid-April 2004 (it was announced on April 1, 2004) when it was hugely popular. I have accounts at a few hundred beta sites and have become quite adept at finding invites for new sites. Now I’m going to reveal my secrets.

1. Mashable Invites is the #1 place to find invites. If the site you want to join is listed, you can receive an invite in minutes. It favors users who have given out the most invites. Having sent out almost 300 invites (292 at my last count), I’m usually listed among the first 5 users, meaning I get invites quickly. You can do the same by giving out invites once you have them from a few popular beta sites.

2. Invite Share is similar to Mashable Invites in that they favor those who invite others, but I’ve had more success with Mashable. The UI is a little hokey (at least in Firefox) and the selection of sites isn’t as large. However, I’ve received a dozen or so invites from here and given out 18.

3. FriendFeed has an invite room where you can request and share invites. Come to think of it, I believe I joined FriendFeed with a beta invite.

4. TechCrunch often gives out a few hundred invites when they cover a new site. You have to be quick though, popular ones go fast (as in minutes after it’s posted).

5. Lifehacker has invites to new sites too, but much less frequently than Techcrunch. Still, if it’s a site you’re interested in joining, then it works great.

6. Twitter is a great source for finding invites because people like to talk about new sites they’ve joined. Search for the name of site you want to join and ask new members for an invite. It helps if you offer invites in return to sweeten the deal.

7. Google search results aren’t as live as Twitter but if the site is a little more mature you may find people who can give you invites.

8. Zewy is a much smaller invite exchange and doesn’t appear to be very active, but it may still work if you’re exhausted the other options.

9. Facebook (or any other online social site) gives you an easy way to request invites from your friends. If they’re invite hounds, they may be able to hook you up.

10. eBay will sometimes have invites for popular sites, if you’re desperate enough to pay for them. This is a last resort unless you have more money than time.