I would say depending on the budget preferably a speaker you can try before you buy, has good reviews, and is not fussy about room placement. Make sure to choose a size that is suitable for your room size and will likely have synergy with your amp. If your amp is on the warm side, probably best not to get warm sounding speaker and vice versa.
Some suggestions would be Klipsch RP500 or 600m for small rooms and apartments if a little on the brighter side works. Very easy to drive, sound great at low listening levels, and bass isn't over bearing. Also have excellent reviews. Steve Guttenberg gave the 600m Product of the Year Award.
Similar to these (Sony SS-CS5) for a lot less money; Cheap Audio Man said they were one of the best sounding speakers to him regardless the price, he said they had a similar sound signature to 600m but he liked the Sony's better. Go figure...
Another excellent choice with sound rearing slightly to the brighter side woud be the Emotiva B1+ Airmotiv speakers. They're a direct online distributer and accept returns if your not happy. They are one of Cheap Audio Man's best bang for buck pics. Super detailed, he liked them better then the higher end Kef bookshelfs everyone raves about. A lot of unbiased reviews on You Tube.
As for a warm sound signature, Wharfedale 1st comes to mind.
Make sure room acoustics are decent before auditioning. Any speaker won't sound great in a poor sounding room. The room is the most important to SQ, then speaker placement, and then synergy of components I believe is how it goes.
Good Luck!
