I am asked questions about parts of this a lot, so I I figured I'd give a rundown of my personal IT setup. I think of it as a personal IT system as the sum is actually more than the parts, and when someone asks what I use for email, or keeping track of things, or phone numbers, or... well, whatever, my answer is always includes an explanation of how it what I use interacts with what else I use. I'll try to keep the explanations geared towards non-technical folks.
At the center of your personal IT system is email. You need to have a primary email address on a domain you own with your mail stored somewhere secure, portable, and with plenty of storage. I use, and highly recommend, Google Apps, Premier. It costs $50/year (per person, which matters if you are setting it up for your family, for instance) and is worth every penny. The webmail interface is the best available, and you can use any email client (outlook, apple mail, thunderbird, etc) you like with it, if you prefer those.
The reasons for GMail (as part of google apps) are that Google is now hosting your data, backing it up, providing a good web based client, providing decent search on it, and providing an SLA on it. That they provide an SLA is a big deal, even if it isn't that great an SLA (99% uptime when I signed up). In addition to this (yes, there is more) other things I use integrate nicely with it, we will see these though, shortly.
Let me re-emphasize the need to own the domain your email is on. You need to be able to change where your email is hosted, or how it is handled at times. If your email is delivered to a domain you do not own, you are at the mercy of the owner to do it for you. In general, this means you will need to get a new email address. I am sure you have gone through the ritual of sending out "please use this new email address for me" messages, and have been on the receiving end of "does this email address still work?" messages. End it, buy a domain and use it for your email. I like gandi.net for handling domains purchases, personally. There are cheaper options, but you are not looking for cheap here, you are looking for reliable and trustworthy.
My wife finally got tired of being my calendar, so I started using the calendar part of Google Apps. It actually works really well, and, to be honest, I am glad I switched from having her remind me of things to using it. I haven't used as many calendaring tools as email tools, but of Notes, Exchange, Zimbra, and Google Calendar, Google Calendar is the clear winner for personal IT.
It hooks cleanly into GMail, which we are already using, supports multiple calendars, sharing (including full scheduing control, though I haven't managed to get my wife to take advantage of this yet), will send email and SMS reminders (SMS reninders are big for me), and other things I use hook into it nicely. Win!
There is the free version, but this comes as part of the Google Apps Premier Edition already mentioned, so I would just go ahead and make use of that one -- it will be all wired up for use with your email, so will make life easier, which is the point.
For a long time I just used a notebook and recopied my lists every day to the new day's page. I hated it, but the fact that I carried my notebook (my externalized memory as I put it, or his brain as my father calls his) everywhere decided this one for me.
When I got my iPhone, this changed. I tried out a variety of iPhone apps (there are probably more TODO variant iPhone apps than anything else), and settled on Appigo's Todo app (somewhere around $10). I actually liked Cultured Code's Things iPhone app more for entry and general use, but Todo won out because it syncs with Remember te Milk, which is the second half of my TODO setup.
Remember the Milk (RTM) is basically a web based TODO list app. I think RTM is much more complicated than it needs to be (it seems to fall prey to the Getting Things Done over-complicated-lists craze), but you can ignore three quarters of it, and it rocks. Again, the data is backed up by them, they provide a decent web interface, and it hooks nicely into Quicksilver (a desktop app for macs which is magical), and more importantly for me, Todo on my phone. You need a Pro account ($25/year) to sync.
The combination of good iphone interface, syncing, and web access are very important for me. As I have now joined the blackberry-wielding hordes who store their memories in their phone, I need to make sure I can get those memories back if the phone goes away, isn't working, or whatever. The web is pretty ubiquitous (and if the web goes way for an extended time, I have much bigger problems).
It bears mentioning that Remember the Milk has its own, free, iPhone app which is quite good and you could probably go with just that. The interactions with Todo (and actually, Things even more so) just roll off my fingers faster, so I use it. If Things adds the ability to sync with RTM I will reevaluate switching to it.
Remember the Milk has very nice integration with Google Calendar, though setting it up when you use Google Calendar On Your Own Domain (the premier edition setup I suggested) is not as smooth as it should be, yet. It also has a decent (basically usable) plugin which you can put in GMail, or a few other places.
I lump these together, but they don't really belong together. I use SMS, it is handy. Not much more to say. I use Adium (on the mac) for IM, and Meebo for ad hoc (ie, someone else's computer) for IM over the web. I also use Meebo (via the web!) for IM on my phone. Meebo's iphone client is better than any of the regular iPhone IM apps I have tried. Both of these are free (yea!).
A nice thing to note, part of the aforementioned google apps is GTalk (Google's IM network, which is mostly compliant with a standard for IM called XMPP). This means you have a GTalk account with your email, which is handy. Making GTalk work with other XMPP things is generaly more work than it is worth, though, unfortunately.
There are other things I use, but these really form the heart of my externalized brain at this point. The key pinciples which drove the setup were that I wanted everything to be internet accessible, externally hosted (so I cannot forget to make backups), and play well with the other pieces. I am very happy to pay for good service, and in the case of Google Apps, am glad I can (as they sometimes have "oops, we deleted your account" issues with the free ones (google is not alone in this, yahoo, hotmail, and everyone else I know of do this too with their free offerings at times).