I have been using Quicksilver (free) as my app launcher for the past few years. I’ve been highly accustomed to it’s abilities and shortcuts, but have grown sick of it’s little bug: pasteboard pops up at random times (for the past year!).
Searching around, I needed to find an app launcher that did what Quicksilver could do, without the crashing. Mainly: an app launcher and pasteboard (something that retains your clipboard history). I also use the Address Book plugin of Quicksilver (to view an Address Book contact without opening Address Book) and use it for quickly searching the web.
Enter Alfred. This is a beautiful application launcher. It’s being updated constantly, adding new feature and refining old ones. The basic feature set of Alfred is free, but the “PowerPack” which adds things like a pasteboard and e-mail/itunes integration. It’s $20, a bit pricey, but I decided to support the company and it’s idea of a regularly updated Mac app launcher.

So far, everything has been working amazingly, with very little preference tweaking. Some cool feature: mini-itunes pop-up window, file system browsing, easy web searches (i.e. amazon, ebay, google, etc), a nice looking pasteboard. It’s fast to search and hasn’t crashed yet (except on my other computer that had Spotlight disabled, worked after enabled).
Also, the company has great support. I was a bit disappointed that I couldn’t view Address Book contact info from Alfred so I twitted “Alfredapp” and got a response in a minute saying it’s in the works.
Overall, I’m very happy with Alfred and highly recommend it to anyone looking to be more efficient on their Mac.