TRIM is a feature that lets the operating system know that space that was occupied by a deleted file is now "open" to accept new data. SSDs work a little differently from hard drives, so features like TRIM help prevent the drive from becoming cluttered with random data. Either way, if your coming from a Core 2 Duo, then any of the new models would be a significant upgrade.
TRIM allows the computer to notify the drive when data blocks don't contain valid data anymore and can thus be safely discarded. There is no way for the drive to determine this by itself, since it does not "understand" file systems like HFS+, FAT, or NTFS. So no, there is no SSD with "inbuilt TRIM".
Modern drives use a process called background garbage collection to improve write performance. This is a complex process that essentially tries to constantly rearrange and consolidate blocks of data to keep memory pages free for future write operations. This largely avoids the deterioration of the write performance over time that many early SSDs suffered from. However, even drives with background garbage collection benefit from TRIM, because it prevents them from unnecessarily copying around stale data blocks and thus reduces the number of memory write cycles. This can prolong the life of the SSD. However, modern drives will still last at least several years under normal conditions.