I second the MGS remake and the Pikmin games whole-heartedly.
Viewtiful Joe (Unless you have a PS2. I think that version is slightly better. I haven't played the second one, but I think it's supposed to be good.)
Super Monkey Ball 1 & 2 (Don't let the premise scare you away. I recommend getting the first one before the second one, but it's not a big deal. If you have a PS2, get Super Monkey Ball Deluxe (I think that's what it's called?) instead.)
Eternal Darkness (Not all that scary in my opinion, but still really good.)
Beyond Good & Evil (Shame it's so short, but you can get it dirt cheap. It's a pity the sequel apparently isn't going to appear, because this was a great game and I'd love to know what happens next. Also, I think the PS2/Xbox/PC versions may have slightly better graphics, but it doesn't make a big difference.)
Ikaruga (Hard, but so good, and very cheap.)
All of these are old, and shouldn't cost you a lot.