Spiceworks is great :) and you can make it feed in data from other sites and stuff now :)
Liberum Help Desk is worth a look but needs windows iis etc
Home - Liberum Help Desk
We use Sysaid. It's not free but it seems to do the job. Also has an iphone, android, windows phone, blackberry app. There is a free version for 2 admins and 100 users. Windows or Linux and completely web based. The paid for versions are based on number of admins, end users etc. It has a remote control as well as a chat facility, knowledge base etc. Seems to work pretty well here.
SysAid - IT Helpdesk and Customer Service Software