Paid for themes and templates? Maybe cheap hosting packages? There may be some free hosting that has an affiliate scheme where you get paid if they upgrade due to lack of bandwidth, etc, you could try that and the clicks/conversions might be better, even if in the long run. Check on the cookie lengths for this as some may only upgrade 6 months later, but is still an idea.
Other networks such as Adbrite, or you could even try to promote the Google Adwords referal program. A lot more bloggers these days seem to be turning more to
SEO and PPC to get their visitors/readers, and some people looking for starter templates have probably never heard of Pay Per Click due to them being new to the industry. I have never tried though so dont know what the conversions are like, maybe somebody else could shed some light on it?
I wouldn't use Adsense on that type of site, the commissions I hear are terrible, hence them being freebies. I see quite a lot of them and they do get decent amounts of traffic so I can understand why you chose to create one. I suppose they are good for linkbaiting too, do you create your own or list other peoples?
Have you had a look at your competitors sites for a few ideas?
What types of themes and templates? All different kind or just aimed at one specific CMS?
Where does most of your traffic come from? Are you aiming globaly or just UK & Eire? What types of organic search terms do you get the most and where from? < means ecommerce templates, wordpress themes, joomla skins, etc?
These are the things I would consider first before trying to find something suitable
Terry