I'm assuming you mean the American Rhythm dance, and not the national dance of Spain.
I'll agree with jlarochelle that Celine Dion a number of good boleros, though personally I think "Falling into You" is a rumba. Probably we're just picking up on different beats. The choice between a bolero and a very slow rumba can be a simple matter of taste and style...find what feels right to you an go with it. Another resource is http://ballroomdancemusic.info/Rhythm/index.htm – the site provides listings of songs by rhythm, artist, strict/non-strict, etc. The lists are made up by different contributors, some of whom are more accurate than others, IMHO. But it's a good place to start. And you can go to amazon.com or bandn.com (or others) and see if the tracks are included in their 30-second previews and whether or not you agree with the list. And there's no "political stuff".... Dancevision.com also lets you preview their music, but I find most of their items are available for less elsewhere.
In any case some pop/no-strict boleros by Celine include "My Heart Will Go On" (to some, her vocals sound very waltz-ish, but the instrument's timing is definitely a 4-beat), "I See Your Smile," and "I Want You to Need Me." Vanessa Williams "Colors of the Wind," Patrick Swayze's "She's Like the Wind," Christian Castro's "Volver a amar," Mambo All-Stars "Beautiful Maria of My Soul" (English Version; the Spanish one is a rumba), Gloria Estefan's "Hablas de mí," "Me voy," and "Volveras;" and Enrique Iglesias' "Por amarte" and "No llores por mi." I understand Ricky Martin has done several, but I don't have any of his stuff.
If you're looking for strict-tempo stuff, I don't think I've ever seen an entire album of it dedicated entirely to bolero music. Doesn't mean they're not out there, though... Usually you can CDs with 2, 3, or maybe even 4 boleros; sometimes there's a CD dedicated to bolero with another dance, such as rumba.
Have fun!
