I don't agree completely with the second post. The main differences in the pre-1830 and post-1830 movements center around their goals and their degree of popular support. Before 1830, as pohnpei states, the main focus was on alternative solutions to the controversy. Compensated emancipation, where slaveowners were paid for their slaves and then they were freed, sometimes to return to Africa, was considered more fair at the time. We had ended slave imports in 1808.
But there is a huge difference in the number of slaves pre and post-1830. In 1800, the US had around 750,000 slaves nationwide. By 1860 that number was an incredible four million, so the nature of slavery, the size of the institution and its location were different in those two time periods.
Lastly, the anti-slavery/abolition movement was more passive and less organized before 1830, and more active and increasingly organized after 1830. As the size of slavery grew, it became more difficult to ignore, and the injustice of it more glaring. Most historians place the start of the modern abolition era at 1831 with the publication of William Lloyd Garrison's The Liberator.
Antislavery before and after 1830.
There must be many comparisons and constrasts that could be made, but I know of only one of them, so this answer is not going to help you much. Before 1830 or so, the antislavery movement was nation-wide and civil. About 1830 or so, northern ablitionists began vitrolic and insulting attacks upon the character and culture of the southern people. Thereafter southerners felt too much hurt and resentment to participate in the antislavery movement; it became an activity of northern radicals and extremists.
Boyd, William M. 1948. "Southerners in the Anti-Slavery Movement, 1800-1830," Phylon, 9, 153-163.
Degler, Carl. 1975. The Other South: Southern Dissenters in teh Nineteenth Century. New York, chapters 2 and 3.
Finnie, Gordon E. 1969. "The Antislavery Movement in the Upper South before 1840," Journal of Southern History, 35, 319-342.
Stampp, Kenneth. 1943. "The Fate of teh Southern Anti-Slavery Movement," Journal of Negro History, 28, 10-22.
Stampp, Kenneth. 1944. "The Southern Refutation of the Pro-Slavery Argument," North Carolina Historical Review, 21, 35-45.
To me, the main difference is that the movement became much more radical after 1830. You can see this just in the fact that it is called "antislavery" before that and "abolitionist" after that.
Before 1830, the main antislavery efforts came from the American Colonization Society. This group wanted to gradually free the slaves (by paying the masters) and then send them to Africa (this is why it was called "colonization"). But after 1830, the movement became more radical. The most noteworthy event was in 1831 when William Lloyd Garrison broke with the American Colonization Society and started publishing The Liberator which called for immediate abolition of slavery.