So - do you read bass clef? If you're going to have to sight read, you'll have to. Just checking.
If you're looking for a melody, check out Wayman Tisdale's tunes...that is, if you're looking for a tune where the bass line is the melody.
As for jazz standard tunes, since you're auditioning for a jazz ensemble, I'd suggest finding a "fake" book that has the melody lines and chord changes of tons of jazz tunes. Find a guitar or piano playing buddy to provide you with the chords and work on it this weekend...don't wing it.
If you have to solo - nail your solo...don't just play whatever comes to mind. If you're an intermediate player, practice your solo to the point that it seems improvised, but is really committed to memory.
Your solo should be your own, and should fit within the chord structure. Remember, space is just as important as notes. A good rule of thumb - if you can sing it, you can play it.
I'm passing this along because you said you are an intermediate player. This may seem difficult, but as an instructor, I've always pushed intermediate players to take the difficult road. If you were accomplished, you wouldn't need to worry about this; if you were a novice, you probably wouldn't even be trying out.
I think your stretch learning is going to be from Cake and XTC to true jazz charts. Walking patterns, classic bass lines (like Red Clay), or jazz tunes that feature bass (like the classic Miles Davis' "So What") will expand your horizons.
Of course, if you really wanted to blow someone away, dig out Stanley Clarke's line from "Hymn of the Seventh Galaxy" when he was with Chick Corea -
http://www.youtube.com/watch?v=DiN8M2ul_9w
As you move forward, here's one of my inspirations -
http://www.youtube.com/watch?v=slAAoTaa-KE
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