You can register with external advertising agencies and place your own advertising on your pages.

XtGem is in no way responsible for the content fill rate or quality of such advertising
Nor is Xtgem in any way responsible for any non payment or suspension of your account with external advertising agencies

First off, register an account on the chosen advertiser's site, then include one of these codes, changing site_id (and zone, in case of mojiva, publisher_id and adspace_id in case of smaato) with your provided account id
You can find these parameters either somewhere on their site while logged in or extract them from one of their provided integration codes (PHP/ASP/etc)

<xt:ad type="admob" site="site_id" />
<xt:ad type="adsense" site="site_id" slotname="slotname" />
<xt:ad type="buzzcity" site="site_id" />
<xt:ad type="inmobi" site="site_id" /> (or type="mkhoj")
<xt:ad type="mojiva" site="site_id" zone="zone" />
<xt:ad type="smaato" site="publisher_id" zone="adspace_id" />
<xt:ad type="admoda" site="site_id" />
<xt:ad type="adultmoda" site="site_id" />
<xt:ad type="webmoblink" site="site_id" />
<xt:ad type="decktrade" site="site_id" />
<xt:ad type="hitcross" uid="site_id" />
<xt:ad type="adiquity" site="site_id" />
<xt:ad type="mobgold" site="site_id" />
You can include as many ad service codes as you want on your site, max one per network and free ads will be returned after the first non-free ad is returned from the service

So for example if you have these codes:

<xt:ad type="admob" site="site_id" />
<xt:ad type="buzzcity" site="site_id" />
<xt:ad type="admob" site="site_id" />

If admob doesn't return an ad, nothing will be displayed in the first code instance and buzzcity code will be executed
If admob does return an ad, buzzcity will not be executed
Second admob instance will not be executed either way, as it's a duplicate call

To insert a second ad on a page insert
adid="2" into the second ad code

It is also very important to note that you might not see ads on your site at all
This is not XtGem's bug! Either your site has not been accepted by the ad network (you can usually check your site's status on ad network's site) or they do not have any ad inventory with targeting matching your country/browser
Despite that, your site visitors might still be seeing ads
It's best to check ad network's site for stats and see if ads are being delivered

You will also find help on the XtGem forum

Advertising agencies will also supply code that you can place on your site to display their ads

NOTE: PHP scripts will not function on standard xtgem accounts And some will not function on upgraded accounts due to php restrictions

If offered use their javascript or Xhtml alternatives

Xtgem does NOT have any connection with nor have I tested any of these sites. Use them at your own risk

MobPartner
Admobix
Clickbank