
iGetcha.org is a suggested opensource and free software directory for the technological sustainability of nonprofits. It's also a simple, non-techie shortlist to assist organizations with a SOHO.
Gmail has become one of the most famous webmails today, and we must say we do love the themes, color collating, the interface, et cetera. Since it has become so popular though, the uptime services and small bugs (ie blank emails being sent) have disappointed once in a while. A bit like Facebook and Twitter, Gmail has experienced the pains of scaling and reliability may be an issue moving forward but we figure the geniuses over there won't let us down ;)

Don't get us wrong, we love Google and everything they offer but if you're worried about downtime, we suggest Yahoo! or ZOHO. Also, check out Gmail offline to compensate for downtime or bad Internet connection.
The most recent cool thing is free phone calls. Combined with with Google Voice, you can call any phone in the US and Canada for FREE! Also, experiment with Google Buzz. Buzz will alert your address book of what your nonprofit is up to, so consider using Buzz as a free software for microblogging your not-for-profit work ;) And, it's also available for your mobile.
Also, check out Chicken's microblog about making Google Buzz more accessible :)