What are ultimate goals for this speaker purchase ? Will this be a garage-man cave rock n roll system ? Do you expect to play challenging, detailed, well recorded music ? What are your musical tastes ?
Various Klipsch models are probably a default choice. Hersey would probably be the sweet spot, as a used pair can be found for less than $500 and are easily modified to sound better (if desired). They are efficient, play to loud db levels, and are very good rock speakers....but not so good with other kinds of music.
If you want a plain head banger pair of speaker, look at Cerwin Vega. Raw, uncouth, unrefined, but excellent for loud raucous music.
MoR option would be a pair of JBL. Many choices for less than $500.
Polk can be hit or miss.
If your tastes are more demanding and you listen to acoustic jazz, classical, etc in addition to Rock, then look for a pair of Triangle Titus 202.
Moderate sized boxes, 91db efficient, benign crossover load, and can play loud when connected to low power tubes (in fact they are an EXCELLENT match with tubes). Outstanding transient response, and reproduction of instruments. Soundstage space in spades. Can sound bright, and no bass below about 75 hz (but will couple well to a sub).
You have a lot of choices.
