Being an Apple user for the last 4 years & I had successfully integrated Mac, iPad & iPhone to my personal & professional life. Many times you will suffer the lack of interfacing to other set of users & devices.. like you can't read SD card from your camera, can't connect your MBA to an ethernet port, connecting MBP to a LCD panel with HDMI & simple things like this.
Over time I had burnt cash to acquire certain set of cables & connectors. You will have always a choice of buying it from apple if you are an early adoptor or wait for OEMs to come up with the same thing at a lower price later..
For iPad/iPhone :
Camera Connection Kit, SQUARE credit card reader, Digital AV adapter
Camera Connection Kit : For reading SD card & Connecting to digital camera/card readers using USB
SQUARE : For taking credit cards from friends who says no cash but card. You may pay a commission if you swipe your Indian card & of course you need an US bank account
Digital AV : Connect to your LCD/projector panel using HDMI. Works well with HDTVs (tested with Sony Bravia & Panasonic Vierra)
For MBP/MBA :
Minidisplay to HDMI, DVI & VGA (all you know). Mono price sells it for very cheap than apple
Of course buy this stuff for MBA or for sure you will be left out without connectivity many times. I am not sure about buying OEM stuff as many complained of having problems. Remember it is just 100MB/s not your giga bit.
The future is going to be super for iOS devices with the introduction of red park cable. You can develop your own devices for your iPad or iPhone.
With the lot of stuff going over cloud, we may not fiddle around with SD, USB etc but there is a long way to go. Same with display tech as well. I am amazed to see videos & music streaming to my Vierra panel with Dlna player for iPad. No cables & it is seemless. Whole new generation of AirPlay enabled devices are coming out as well.
The future is going to be awesome with less connectors to carry around