should i buy it?

[Adam]

no specific section on this site listing options but most know the options so just ask

std seat options (both in smooth valcona leather all over)

1. RS4 bucket seats - electric lumbar and side bolsters that inflate when sport button is pressed.
2. Recaro sports seats - all electric adjustment but you lose the side bolster inflation

Which is best - do a search as there has been much discussion, brief unbiased summary of plus points:
Buckets - the real McCoy and one of the signature features of the car, look better, hold you better
Recaros - full electric adj (but heavier), some find more comfortable esp if they have back issues, easier to get in/out of car, slightly improved rear legroom, wear better

best options - no such thing really hence they are optional but here is what to look out for:

satnav is the ONLY must have - in pre-07 cars this was generally specced as the tech pack (as it saved you £300 on the separate option costs) and comes bundled with adaptive lights (they swivel when you turn the wheel) and a CD changer in the glovebox. 07 / 57 cars took advantage of the £500 cost for DVD satnav across the A4 range so tech pack did not exist. In the later car I would say it is desirable to still have the adaptive lights and either CD changer or ipod connector (opinions differ but the ipod connector is pretty awful to use and the car comes as std with SD card slots for mp3 playback).

other options that most would regard as desirable but not essential

auto dim mirrors / wipers / lights pack
sunroof
TV reception
front armrest (no cost option)

options you need to be careful of:

optics pack (removes all the chrome from exterior has black trim instead) - depends on colour of car and taste (mine is black and for me this option was a must-have as i think it looks much more puroseful without the chrome but you need to compare with/without)
bluetooth/GSM prep - beware because this means you will either have an ugly and unnecessary phone cradle on your dash or will lose the proper RS4 wheel (for me this was a must not have for those reasons but I will retrofit this some time for no extra cost and without the downsides mentioned)
sports suspension plus - firmer ride, 10mm lower - some could find too harsh, some will like

other options that are nice to have but add little value, not at all essential

rear bum warmers
rear sideguard
black suede finish to wheel/gearknob
rear blinds
floor mats (get Audi to chuck them in)
auto air recirculation for the aircon
auto open for boot lid
coolbox in glovebox

[Dom81]

Excellent summary

My only additions / comments would be

Recaros - significantly improved rear legroom. There are two choices of leather - metallic valcona (from memory) or silk nappa. Both look virtually identical, but the nappa has contrast piping
Front armrest - can be as much of a pain as a benefit. It's a sports car not a sofa after all...
Privacy Glass - a bit like the optics pack. With the right colour car it can look excellent - especially on Avants
Colour - Best bet is to go stealth or in-you-face (if you're brave) - the intermediate colours are less popular
Trim - Carbon is the signature dash, Alu only if you don't like dark interiors