Andre3k, you never mentioned whether you have other portables, or are even considering them as an option.
If you don't have anything from the last 5 years, then a GBA SP would be the best bet. You get a wide selection of games from that platform alone plus the back catalogue of the previous iterations, and it's much more cost-friendly compared to the DS.
I'd be surprised if more than half of those upcoming DS games listed will make it out this year, but overall the DS still has a impressive lineup for the rest of the year, and dare I say a better one that the PSP. Of course, the potential "killer apps" for the DS like Metroid Prime or Animal Crossing won't be coming out until fall at the earliest, so unless the current lineup strikes your fancy then you might as well put it off until the software you're interested in finally arrives.
Game library probably isn't the best reason to get a PSP right now. Sports and racing seems to be the only significantly represented genres so far, and the bigger releases like Grand Theft Auto are at least a few months away. I'm not sure when the first game like ICO or Gran Turismo 3 will come out that shows off the power of the system, so it may be a while before we see much of the PSP's gaming potential.
One thing that PSP has over the DS right now is that some games are already playable online. If the PSP's overall internet technology is similar to how it is in Gretzky NHL, though, it's somewhat mitigated by the fact that it's implemented pretty awfully in the PSP so far. It appears that Animal Crossing and Mario Kart are gonna be the first online wireless games for the DS, so if Nintendo can get the technology right by then, kudos.
Legalities aside, the PSP is turning out to be nicely hackable. If emulation is your thing, there's already an impressive amoutn of material out there (unless you already updated your firmware.)
A PSP is a waste of money if you're thinking about it in terms of MP3s. For the same price as a PSP and a 1GB card, you buy at least a 40GB iPod. I doubt this will be a toy for serious music fans.
I would have rated video as the least of my priorities several months ago, but now that I've seen it in action, I think I'll be putting a comparable amount of time into that as with gaming. The Spider-Man 2 pack-in sold me on the UMD video quality, but I don't like the prices - too used to paying cheap prices for DVDs. Still, right now in my life I'm finding that I have more time to use portables than watch DVDs at home so if I find some good deals on film UMDs I'll probably stock up. Playing video off a memory stick intrigues me even more. I don't have a 1GB stick yet to do some serious tests, but from the clips I've converted and copied over so far, even some of the lower encoding levels are more than adequate for my liking. I probably need about another month or two to see if I'd give this feature a full endorsement, but my initial impressions are even better than I thought they'd be.
So in summary, MP3 nay, video yay, and games ehh. If you do get one, there's probably at least a couple of games you'll be interested in, but you can easily wait on buying the system unless you've already made up your mind. Exciting piece of technology for sure, but we'll see how Sony builds on it.