The main thing to remember about being a Sorcerer is that they have very few spells know, but can draw their spells from a broader selection than the Wizard. That means they can learn a few Cleric and Druid spells on top of the Wizard spells. Everyone always seems to miss this line item in the character description, but it's there and it definitely makes a difference.
Most people miss it because it's not actually stated anywhere ever. Some people claim that it is implied, but that's as far as it goes.
Personally, I wouldn't allow it, since giving a primary caster access to the spell lists of non-primary casters (Bard, Ranger, Paladin) is probably a recipe for broken.
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Here's what I did for Sorcerers in my game:
Sorcerers have Use Magic Device as a class skill, gain Eschew Materials at 1st level, and gain bonus feats at 5th, 10th, 15th and 20th level. Their bonus feat can be any Metamagic Feat, any Spell Focus, Spell Thematics (FRCS post-errata version) or Improved Familiar. Also, they get extra spell-slots at odd levels, gaining a "0" (bonus spell-slots only) in the level above their highest current known spell level. Any higher-level spell-slot can be used for metamagic, or to cast any lower-level spell as usual.
The effect of that last bit -- "0" (bonus spell-slots only) at odd levels -- is to allow them into spellcasting PrCs at the same level as a Wizard. It won't help them if the PrC demands that they know a specific spell, but it will help with requirements like "able to cast 3rd level spells".
Cheers, -- N