If you need to run a quick (and free) scan of your site to make sure that it is not infected in any serious way, I recommend you try out Sucuri's Free Malware Scanner (sitecheck.sucuri.net/scanner).
For ongoing maintenance, a few plugins that I use on my project and personal sites are:
- Wordfense
- Better WP Security
- CloudFlare (for help in preventing known malicious traffic from even hitting your site)