Melf's Acid Arrow:

Dealing acid damage, this spell is nifty for finishing off Trolls. Lasting several rounds as well, it can also serve to disrupt enemy Mages' spellcasting. When your Sorcerer reaches level 20, the spell does a minimum damage of 14, average damage of 28, and maximum damage of 56. Not bad for a level 2 spell.

Mirror Image:

Since you are soloing, you have no super strong tanks to rely on, so you will need to minimise hits on yourself.

Knock:

No Thieves.

Resist Fear:

A scared solo Sorcerer... is a dead Sorcerer... ...

Web:

If you have the Ring of Free Action, blast the very area beneath your feet with 6 Webs and laugh as your enemies struggle to move. Proceed to kill them at your leisure.

Detect Invisibility:

Bite the bullet until you get True Sight

Blur:

Although the -3 to AC bonus sounds good, think about it, how often is your Sorcerer going to be engaged in melee combat? And if you are concerned about enemy archers, Stoneskin will always protect you. This spell better serves Fighter/Mages and Bards, your Sorcerer does not need it.

Aganazzar's Scorcher:

Pretty cool spell, but the damage is pitiful against high level enemies.