Big attachment solution: SendAlong lets you send files of any size with your email. No installatioin required, no spyware, Free trial. PipeBytes is an alternative, it's more bittorrent-like.
Email-tracking solution: SpyPig sends you a notice when a person has opened your email. You can choose different tracking images, including a complete blank one, which makes it impossible for the receiver to discover that you're trying to track the email.
If you are like me, that is, a total social person, you should give socialthing a try. It lets you see a stream of content updates from your social networks: digg, facebook, twitter, lastfm, delicioius, pownce, you name it. Whenever your friend has a new update in any of these accounts, you'll get noticed in your "lifestream". So without checking all of the websites, socialthing keeps you notified of everything happening in your network. It's just sweet!
PresentationYes, it's true that there are a number of impressive online presentation makers: Google, Zoho are the big ones, with a complete set of office equivalent web tools. But in terms of presentation, Empressr is easily the best - interactive, powerful, and deals with graphics really well.
Sketchcast is actually a recorder for your sketching process, but I find it useful when doing a presentation too.
Graphic EditingI have yet to decide between Graphita , Splashup and Picnik, all three are nicely designed, and useful in their own way.
CollaboratingTo-do lists, stick-its, photos and documents, everything is just beautifully incorporated with Stixy. It's THE nicest online collaboration tool I've used. Give it a try.
Website BuildingDoodlekit, it's the best free website builder I can find.