Sometimes you want to send emails to a whole group of clients and are worried about spam filters blocking them.

There's a list of words and phrases which trigger spam filters here...
http://www.refreshedmedia.com/online-marketing/words-that-trigger-spam-filters.htm

...and a list of not-so-obvious words which also do this here...
http://www.directmag.com/disciplines/email/words_trigger_filters/

There's no way to guarantee an email will beat spam filters because they are customized to suit the user, and the better ones work by learning the kind of emails you want and don't want over time (Bayesian filters - http://email.about.com/cs/bayesianfilters/a/bayesian_filter.htm ), so there's an element of pot luck about it.

Best bet may be to just send them, requesting a read receipt, and mop up those that bounce or where you don't receive the read receipt later.

*Update 20/10/06*
Tips from PC Magazine:
Take These Steps to Avoid Spam Purgatory