Sorry, I realized that the number of answers were exploding, so I'm rather collecting my remaining proposals here. For discussion feel free to add more answer posts.
transaction-selection – Questions about what criteria influence the selection of unconfirmed transactions for block inclusion.
transaction-id – The unique identifier of a transaction corresponding to the sha256d hash of the transaction.
non-standard-transaction – Transactions which deviate from the standard transactions created by BitcoinCore yet are valid. Non-standard transactions can have other redemption scripts than transactions to a public key, e.g. redeemable by password, multi-signature, any signature, checking external states, and more.
reverse-transaction – Questions relating to how particular transactions can be undone or replaced.
transaction-propagation – Questions about the manner, speed and incentives of relaying transactions in the Bitcoin network.
transaction-input – Questions about the mechanics of redeeming a UTXO in an input script.
offline-transactions – Questions about transmitting bitcoins without the wallet being connected to the Bitcoin network.
script – Within the context of Bitcoin, scripts are a set of instructions on how to complete a transaction. The default send/receive actions are scripts but the protocol can be extended through the creation of new scripts, such as the DNS replacement abilities of NameCoin.
output ← This still needs a wiki excerpt, perhaps should be merged into another tag.
mempool ← Needs a wiki excerpt.