Seems a lot of you like all-in-one solutions, meaning software that will handle playback of both audio and video content. Personally, I prefer to use specific tools for specific tasks. I'm not a fan of jack-of-all-trades solutions, in other words.
Besides, none of the suggested all-in-one players have native Last.fm support.
For video, my current favorite is GOM Player. It has codecs built-in and plays just about anything I throw at it. It's even better than VLC, and I've never liked VLC. It seems to be very popular in general, but I've always hated VLC's interface. I still don't understand who came up with the idea to code the progress bar the way it's implemented. Click on a spot to jump to it while playing video, and it will jump, but hardly anywhere near where you clicked. It seems to arbitrarily jump in predefined increments, so you never really know just where it will land. This has always struck me as very strange behavior, not at last because it is different from just about every other media player I've ever used.
I was a big fan of musikCube, but its development came to a halt quite a while ago and has been stuck at v1.0. I haven't checked their site in ages, but I really don't like using software that is out of development. Otherwise it would be just about the best music player I can imagine.
I've used XMPlay before and must admit that it is a very fine audio player. It's impressively light on resources, (not that I have to worry about that anymore with my new machine, heh, but it's always a plus) and quite full featured.
I like what I see with VUPlayer but have not tried it yet. It's default UI looks rather ugly, but if it will let me do the things I want to do, that's ok.
ALSong is another cool option that I've always wanted to try out. Now even more after reading the comments about the great way it implements the playlist.. but if that's the only thing to set it apart from the rest of the pack, I'm not sure that point alone will convince me of its greatness.
The whole point of trying to find an alternative here lies in the player an alternative is being sought for: iTunes. As such, solutions such as WMP11, Realplayer or WinAmp don't really make sense, seeing as how they are all big multimedia apps that are clunky and often have a "heavy" feel attached to them, just like iTunes. The ALSong, VUPlayer, Foobar, XMPlay and the other similar players seem much closer to the solution.
BTW, I've tried Foobar on multiple occasions, and while I thought the idea of making such a highly customizable player is cool, I always ditched it after a while because it forced me to do far more customizing away from the defaults than I cared for. Foobar is like Firefox. It's ok by default, but to make it great you have to customize the living crap out of it. Not a huge fan of that.. I like the product I use to be solid out of the box and to be efficient and easy to use as well as full-featured right from the start. I can't say I find Foobar fitting that bill (nor does Firefox AFAIAC).
Thanks for the suggestions everyone!