Any gambling-related articles are ok. If you like poker and your site is related to poker, then that would be a topic for you.
Here is how it should work… (and how others are doing it on the site):
YOUR KEYWORD (for a page on your site) is: Texas Holdem
Your Article Title should be: Texas Holdem – Strategies and Rules
Your Article Copy should have:
an H1 Tag: Texas Holdem
an H2 Tag: Strategies and Rules for Texas Holdem
an italics word in the copy: Texas Holdem
A link IN THE COPY: With title, Texas Holdem, link anchor Texas Holdem
At the end…. IN BOLD, Texas Holdem
While that might seem a bit extreme, it works well if your copy is at least 3 quality paragraphs. You do not want to spam, you just want to create a clear and concise article to the search engines. This article, as defined above, is clearly an article about???? You guessed it, Texas Holdem 
And that article points to your site while creating a LINK that is 100% on topic.
So – any article you want. Slots Rules, Blackjack strategies, Casinos that suck, anything you want. Just keep the direct Affiliate links out of it and point it towards your site.