Interestingly, the choices in the "3-9x40 or similar" category expand considerably in the <$300 range, also there is a very nice tweener available.  However, as far as other scope types go, there isn't all that much that is really worthwhile.  One exception to that is that for $300 you can get the cheapest "tactical" scope I feel comfortable recommending.

Variables:

Bushnell Elite 3-9x40

Weaver Grand Slam 3-10x40

Vortex Viper 3-9x40

Vortex Viper 2-7x32 (one of my favourite tweeners)

Nikon Monarch 2-8x32

Nikon Monarch African 1-4x20

Fixed Power (hunting):

Leupold FX-II 4x33 and 6x36

Tactical:

SWFA S.S. 10x42

Ultimately, in this price range, two scopes really stand out: SWFA S.S. 10x42 and Vortex Viper 2-7x32.  The first is an exceptionally robust tactical scope that can focus as close as 10 yards.  It is suitable for anything from a precision rimfire to 50BMG.  The second is an exceptionally nice tweener scope that works well on almost any hunting rifle.